Hi there!
In terms of avoiding distraction - for me, it's all about removing the distracting source. So, that usually involves putting my phone on do not disturb and putting it in another room or somewhere completely out of reach. If I need to use my laptop, I make sure I'm logged out of social media and only open tabs relevant to what I have to do. If I don't need my laptop, that goes away as well, and I clear my desk as well as I can so the only thing in front of me is what I actually have to do. That way, I force myself to do it. I think different things work for different people, but I find that removing distraction is the best and easiest way to avoid it.

In terms of motivation - I'm not the biggest fan of motivation. If you rely on motivation to let you do everything, you're not gonna get much done. I've been waiting for motivation to fall out of a tree and hit me on the head for a while, and it hasn't yet haha. Don't get me wrong - sometimes, I get really keen to do some stuff. But motivation is never constant, it's always fleeting.
What's more important is self-discipline, and starting something and persevering until the job's done. Plus, usually you'll find once you start something, it's not so hard or bad to keep on doing it - it's just starting it that's the pain. So maybe break stuff down into smaller tasks, and that makes it more achievable. So, for example, say you want to write a practice essay for English, set yourself something like:
- I'm going to write my introduction, and not leave my desk till I do it
- Now I've done the intro, I'm going to write my 1st body para, and so on and so forth
Regarding procrastination, maybe ask yourself the pros and cons of whatever it is you want to do - so like, weigh up and consider whether it's really a good thing to procrastinate. Otherwise, probably follow some advice I read from Brenden once (will see if I can find the link to his post) - it's basically that you should like, procrastinate until you don't want to procrastinate anymore. You'll find that you'll get sick of it, and then, you won't want to do it, so you'll be able to smash out some work. Might not be the ideal answer you're looking for, but like, it probably works. Plus, probably also try to think to yourself - "why am I procrastinating?" - is it because you're anxious? Is it because it's just not a particularly fun task? I think once you understand the root cause a bit better, you can tackle that procrastination.
I guess also, maybe review your study schedule? As in, if you leave homework till night time, maybe try doing it when you get home, because that way, you have plenty of time to do it, and you'll probably have the whole evening to relax and do fun non-school stuff!

Plus, just want to chuck in a reminder to make time for leisure stuff - studying all the time can be pretty counterproductive.
All the best! I hope this has helped a bit.
Finding out the best study methods for you is often just a process of trial and error