For new competitive Pokemon battlers

First, this is the most easily recognized format for sharing and rating teams.
<Pokemon> @ <item>
Ability: <ability>
EVs: <ev> HP/<ev> Atk/<ev> Def/<ev> SpA/<ev> SpD/<ev> Spe
<nature> Nature
-<move>
-<move>
-<move>
-<move>
<explanation>

A few basic tips:

1. Don't use mixed attackers unless you really know what you're doing. The first advantage of attacking using only one stat is that you can max out just one attack stat and either HP or speed, greatly increasing the chance of your Pokemon taking a hit or moving first. The second advantage is explained here on PokemonDB."In most cases it is preferable to have a nature that decreases either Attack or Special Attack for Pokémon whose strengths are the opposite type of attack. Espeon, for example, favours Special moves, so it's best to use a nature that decreases its Attack since it won't be used."

2. Don't use 2-turn moves unless you really know what you're doing. They offer the foe a free switch.

3. Usually, you should max out your 2 most critical stats. It doesn't help very much to spread EVs around. For sweepers, it would be an attack and speed. For tanks, it would be HP and an attack. For walls, it would be HP and a defense. For support, it could be HP, either defense, or speed, depending on which moves it's using.

4. If you aren't using a mixed attacker, it's almost always better to go with the Pokemon's highest base attack stat. In other words, don't use physical Blissey.

5. It's often a bad idea to have 2 moves of the same type on the same Pokemon. You only have so many slots for coverage attacks or support moves.

6. Try not to have too many Pokemon with similar typing or stat spreads. It makes your team easier to sweep.

7. Don't give leftovers to your sweepers. They tend not to last very long, so 1/16 of their HP per turn isn't much of a help. Life orbs, choice items, expert belts, or focus sashes are almost always better options, despite negative effects from some of them.

8. Don't use advice that doesn't make sense to you. They're your Pokemon, your teams, and your battles, not mine.

For the mechanics behind Pokemon battling, visit bulbapedia.bulbagarden.net
For more detailed competitive battling advice, visit smogon.com

Last updated 12/16/2015.