Lately I've been noticing a lot of speedrunners with bad habits and mentalities that are hurting their ability to improve, which often leads to runners struggling to PB even though their time isn't considered "good." There are many easy steps you can take to become a better speedrunner and significantly increase your rate of improvement. This is mainly targeted at lower/mid level runners and new runners, but this advice can help any runner regardless of skill level (although most good runners probably already know most of this).
Probably the single biggest and most common mistake many speedrunners make is endlessly grinding runs without ever taking time out to practice or learn new things. If all you do is grind runs, your improvement will likely be very slow and you will struggle to PB even though your time is significantly slower than what a "good time" would be.
When you're learning a new game, the start of doing runs is NOT the end of your learning. Chances are you're probably not using all of the best strats when you start out, which is perfectly acceptable since some things might be a bit too hard for beginners, but make sure you learn them eventually. You should make an active attempt to learn new strats frequently until you know that you're doing everything the fastest known way possible. Using new strats is one of the easiest ways to save time in a speedrun because it has nothing to do with playing better or worse, it's just doing something differently, so you should take full advantage of that.
Do not grind runs forever without ever practicing outside of runs. Some people seem to think that just doing a lot of runs will eventually make you improve, and it can, but practice will help you improve much more and much quicker than just grinding runs ever will. You will repeat sections much more frequently and efficiently in practice, and the fact that you're not in the middle of a run means you can try new stuff and experiment without throwing away your run. I know some people just want to grind runs because its more fun than practice, and that can be true, but do you think you'll have more fun grinding runs and improving very slowly if at all, or taking some time to practice and improve much quicker? And once you get in the habit of practicing a lot, it will become fun because you will know how significant the benefits from it are.
When practicing, the goal should not be to do the same thing repeatedly, it's to do the same thing repeatedly faster than you did it before. Comparing against your sum of best is really good for practice, your goal should be to get as close to you best as possible as consistently as possible, not just being able to get through a section consistently.
Many people will say that when you start running a game, your immediate goal shouldn't be world record, which can be good so you just focus on learning and having fun, but don't go into it thinking you will never get world record. Even if you don't end up ever going for it, starting out thinking that you will never get it immediately sets your goal much lower than what you could get. Don't think that you'll never make it because you think you "suck at games," everyone sucked when they started and got good through learning and practice, you have no reason at all to think you can't get good.
Do not be intimidated by hard tricks. Hard tricks are often not nearly as hard as they might seem at first with some practice and learning about the trick. If you try it a lot and just can't seem to get it, it's ok to put it off, but come back to it at some point relatively soon. You might find a trick to be really hard when first attempting it, but really easy when revisiting it a month later just due to generally improving and understanding the game better. If you really can't seem to do a trick, try looking for a way to make it easier or somehow modify the strat to something you might be more comfortable with. The way everyone else does it might not always be the best way. Sometimes a hard trick will require a huge amount of practice, but if it really saves a lot of time, it will be rewarding when you can do it.
When learning tricks, don't just learn how to do them, learn how they work. Figure out exactly how tight the timing is, or how precise the angle or positioning is, and learn why it is that way. Learn the mechanics behind why tricks work. If you understand how the trick works and not just how to do it, you will have a much easier time learning it, and might even be able to modify the strat or make your own based on what you know about the trick.
Just learning all the big tricks doesn't make you fast. The small details, mainly movement, are incredibly important and can add up very fast, especially for longer runs. Movement is often cited as the biggest difference between the top level runners and lower level runners. Movement can be difficult, but is often overcomplicated. Movement is simply routing at the smallest scale. When you route how to cross a single room or a single area, that is movement. If you go into an area and just think "go from here to there" without thinking of the specifics, there's a good chance you might suffer from bad movement (assuming your games movement is more than hold forward/right). Look at all of your options for movement in every single area and pay attention to every little detail in how you move and your movement will be significantly better. Just having a very specific plan for all of your movement helps a huge amount.
Do your own research for tricks and strats. Don't expect other runners or glitch hunters to find everything for you, make an effort to try to find stuff yourself. Never assume your game is already 100% optimal and try thinking of ways to improve it. It doesn't need to be huge new glitches, it can be something as small as taking a different path through a room. Try to think of portions of the run that just don't feel like they're as fast as they could be. Think of all of your available options and see if anything different than the regular strat could be faster. Also, if you have an idea for a new strat that you think is faster and someone else tells you its been tested and it slower, test it anyway! Incorrect timing and testing happens surprisingly often and is worth another try if you really think it should be faster. Even if you never end up finding anything useful, just looking for things and thinking about the game can help you at least learn more about the game and why you do what you already do, which can be useful itself.
If you know a runner who may suffer from some of these bad habits and mentalities that I have listed here, please tell them to read this! I feel like a lot of people are approaching speedrunning the wrong way and suffering from it, and I want to see more people making an effort to get better. I want endless run grinding with no practice, learning or researching to end.
Practicing is very important and grinding runs without practice is very bad
Keep learning stuff until you have nothing left to learn, and then look for new stuff
Don't just learn how to do the speedrun, learn about the game
Look for new things on your own, don't always depend on other people to find new stuff and never assume there's nothing left to find
Don't be scared of hard tricks, they're probably not as hard as they might seem at first
Movement is just small scale routing, route your minor movement parts and it will make your movement much better
Everyone sucked before they got good and you are no different, have some confidence in yourself
I'm a bad writer so a lot of this is probably poorly written or can be formatted better, feel free to tell me any improvements to this.