Pacra's Abyssal Knight guide - DCSS

They're a great melee class, equally adaptable for heavy armour fighting or fighting with the usual charms backups.
Conjuring or summoning works as well if you get an early book, my SpAK turned into a summoner (and my streak breaker was a conjurer, I think.)
Lugonu is easily one of the most powerful gods, with abilities that get your character rolling fairly fast - at ****** you should never die, unless of course to user error/hubris.

First, I'll give a rundown of Lugonu abilities, then an overview of early/mid/late/extended game.

 Lugonu abilities

Depart the Abyss - Self-explanatory. When you start the game DO THIS IMMEDIATELY, anything up to and including executioners and invisible lorocyprocas can inhabit your abyss entry outside of your LOS.
An AK (at least a streaking one) ignores the abyss as much as possible (which of course, is one of the main draws of worshipping Lucy.)

Bend Space - For a 1d4 hit point loss, randomly blink. Just like the spell, except it takes 1 mp instead of 2, a bit of health off, cannot be controlled in any way, and can sometimes blink and damage nearby enemies (the damage isn't noticeable, in my experience.) Be forewarned, if you blink with only 1-4 hp left, you will die from the damage and not get a warning message! This spell is not very good when you get it early due to the damage incurred and should be used sparingly. It's decent for getting away from things in the Lair and onwards though, just like regular blink. Don't forget about it (like me) because it can sometimes save your hide.

Banish - For 4mp and some piety, banish a monster to the abyss. This ability is great and what you should be working towards as soon as you start your character. Ogres, centaurs, hill giants, and orc warriors are your first targets. Hydrae and komodo dragons in the Lair are your next. Spiny worms, ettins, and shadow dragons later on. And of course, anything that you don't want to deal with or start a fight with. Remember that anything you banish will end up in Abyss:1, which can make your final ability risky; don't abyss something if you can easily kill it instead (especially because you only get half xp for banishment.) One other amazing thing about banishment - many early uniques don't have much magic resistance, and the vast majority of ghosts don't either. Almost all ghosts before vaults can easily be banished with enough invo, same for uniques. For those uniques you can't easily banish, use the following ability:

Corrupt - My favorite god ability in the game. For a decent piety chunk, warps the level immediately around you and calls in a metric fuckload of demons, undead, and abyss-themed monsters, all of which are neutral and will attack anything around. They will not target you unless they are specifically trying to move into your square, or you attack them first. Use this in one of two situations: a) you are about to get in a fight that you know you can't win, or b) a powerful unique shows up and you need to get past it/get its weapon, while (a) might apply as well. It's extremely powerful and at decent Invo skill, can kill just about -anything- in the game - boris, mennas, orbs of fire, antaeus, you name it. Drawbacks - takes a bit of HP off (five) and a good deal of food; you are usually surrounded by neutral abyss monsters, leaving you unable to move - you'll want to blink (via lucy or otherwise) or teleport; you'll want to have hp to tank occasional neutral attacks. You also get no XP for any kills made by corruption-summoned creatures (although hilariously enough, you still get Henzell/Sizzell/Gretell unique-kill shoutouts in your online games when corruption kills them.) Also, you can corrupt once per dungeon level.

Enter the Abyss - Your second 'oh shit' card. Use this when you were too dumb to use corruption starting out a fight and you're in serious, going-to-die-in-the-next-turn-or-two situations. Will take a huge piety chunk off and potentially reduce your current HP/MP to 1 (DO NOT USE IT WHEN POISONED ARGH.) Also reduces your -max- hp and mp, kind of like borgjnor's revivication. You can see why it's only used in the most dire of situations. When you get into the abyss, you'll want to use whatever healing stuff you have at your disposal - regen rings get put on, regen spell gets cast, healwounds gets drunk/zapped, even curing. Waiting in abyss:1 is fairly dangerous since literally anything can wander into you trying to heal up - including all that stuff you banished. You might want to get deeper into abyss:2 if you know you've abyssed some very strong things you don't want to run into. Remember that once you leave the abyss, you'll end up right back where you abyssed yourself, so if you are healed up and feel up to exploring the abyss for items/piety/xp/the rune, do so and when you go back, things may have wandered off, like a ghetto chei Step From Time. In any case, be prepared to encounter the same situation you escaped from!

Corrupt weapon - Pray at an altar to have your wielded weapon given the distortion brand. You shouldn't actually use this except in very specific circumstances: a) you are speedrunning. b) you are planning on ninjaing the orb far in advance, c) you are playing a caster that doesn't want to really melee one bit, d) you haven't found any good weapon or brand in forever and are really hurting for extra melee damage. The distortion brand is good early on, and extremely powerful for speedruns, ninjas, and pure casters, but if you're playing melee-centric AKs, it's quite bad. It sometimes teleports whatever you're fighting, which is very annoying if you had them damaged quite a bit, forcing you to perhaps go look for them; worse, it frequently blinks enemies away from you, and the further you progress into the game, the more enemies there are that have painful ranged attacks (close to the majority of monsters at the end of the game.) Since you're trying to kill things to actively avoid their potential damage output to you, you can see why this is a bad idea. Also distocleave is absolutely awful.

Lugonu is a very passive god after you get to the point where you aren't banishing every threat that comes along. After banishment loses its appeal, you have a god that helps you ignore things you hate dealing with like spiny worms, and will save your bacon in annoying/tough/dire situations (blink/corrupt/enterabyss.)

 Early game guide

Turn off all skills except your weapon skill and Invocations. Invocations will auto-turn on after you get 1 star again since you departed the abyss and lost it. Your +2 weapon will make d:1 a breeze. Run away from anything as strong as or stronger than a gnoll. Really, run away from anything you aren't absolutely sure you can kill without getting into the single digits. Rest to full after every fight. Pick up as many daggers/clubs/hand axes as you can and throw them at enemies before engaging in melee, especially on d:1. Play focused, pillar dance if you need to, always explore carefully and leave escape routes planned out in advance, explore by circling around so you always leave a pillar dance corridor or area open, never over-extend yourself into uncharted territory and do not rely on autoexplore. Autoexplore has its uses when you are diesel or are overleved for your location, but can kill lazy players fast. Same with tab. Wear the armour that gives you the best combined total of ac/ev, sometimes even if you are going dodging you'll want to wear heavy armour to start out - choose wisely. You are trying to get banishment castable at around 11-20% by the time you get it, which should definitely be attainable if you play smart, play slow, don't take risks, use-identify scrolls/potions/wands after every cleared level. You may want to take downstairs and upstairs when you see them to determine if they're decent escape routes. Once you get banishment, backtrack and banish everything you avoided/excluded on the map for xp. When you get to the Lair entrance (don't even go into Orc), you should have some decent weapon skill and at least 10 Invocations skill - if not you are doing something wrong. You'll want to leave Invo on in the Lair until around 13. (While you're in lair, you can also start turning on fighting and dodging/heavy armour or spellstuff if you found a decent book.) Good thing about Invocations - no race has awful invo, even -1 aptitude is absolutely doable. At 13 skill you can reliably oneshot-banish hydrae and other things. Death Yaks are NOT easily banishable, you'll want to run from them. If you get to Lair, congrats, you should be able to win the game if you don't make stupid mistakes.
A quick addendum on sewer/bailey/ossuary portals: do them, especially if you have banishment. You can kill the small threats and banish the large ones, up to and including orc knights, and then reap the rewards (of course, you won't be able to get anything the banished were carrying.)
Another addendum on acquirement: your first acquirement should -always- be weapon as an AK. Other acquirements should be either armour (or wand if going heavy armour for hastewand.)

Mid game guide
I term everything after Lair and before Vaults:5 'midgame'.
Orc is incredibly fun and easy as a Lugonite. Simply do Orc as usual, you should be buff for orcs from the Lair. You should be able to tango with orc warriors by now, if not, just banish them and sacrifice the rest. Get as close to the orc:4 shop vault as you dare, use Corruption, run away and wait. Bam, you get four shops for free!!!
Be careful in the Vaults, a lot of things are there that resist easy banishment (not yaktaurs, thankfully). For the Lair runes, you should have no problem, especially since you can corrupt the rune vault. By the way, banish things like Saint Roka, harold, joseph, josephine, terence, sigmund, grinder, prince ribbit; corrupt things like boris, mennas, lamia, frederick, arachne, ilsiuw, aizul, rupert. Honestly the hardest part of the game for an AK is before Lair.

 Late game guide
Banish shadow dragons if you're heavy armour to save xp. Corrupt when you overextend yourself. Banish yourself if absolutely necessary. Take Zot slow, clear everything, priority-banish moths of wrath, make sure you have a haste wand if you're heavy armour or can cast haste if you're dodging. Ninja-ing the orb is eminently possible with a judicious Corruption use, however in my streak I killdudesed Zot:5 every time since I'm much more comfortable in a streak doing that.
Addendum: a well-placed Corruption will wipe out the entire Elf:3 deep elf vault and, depending on the vault, open up the loot piles for easy access!

 Extended guide

If you've gotten this far and intend to do it I shouldn't have to tell you what to do! Banishment will be useless except for taking care of annoying neqoxecs. Use Corruption on hellpanlord rune vaults, apport rune, teleport out or otherwise leave. Corruption is obviously really really good for Tomb, letting you skip an entire level of it. Abyssal rune is easy when you can escape at any time. You can also use corruption to get the slimy rune before ever killing the royal jelly! Corruption isn't very good against TRJ in my experience unless you're meleeing it at the same time; your mileage will vary.

That's it off the top of my head, I'll edit if I remember anything else to add.