It'll probably depend on what you have, struggle with, and what you need to change.
If you're mainly dealing with depression, then you'll have a different plan than if your main issue was an anxiety disorder. Similarly, having addiction or trauma changes things around too. Have you ever been diagnosed or seen a mental health professional before?
Then there's the severity of your problems. Are you able to go outside and be independent? Do you work or go to school? If your mental health issues significantly impair your life then you need to be careful about what you do. If you are having trouble attending to your basic needs, you need to start there before you try the typical self-care stuff like meditating or joining a knitting club, since taking good care of yourself tends to give you the most relief and improvement quickly. Also it's easy to get overwhelmed and give up on the harder parts of recovery if you can't do the little steps first. This part is mostly relevant to more severe cases of anxiety or depression though, idk if thats the condition you're in.
Whether or not you know what you have, I think a CBT workbook + journalling is always helpful, especially for depression. There's lots of free workbooks on libgen for all sorts of circumstances and topics. Try to catalouge all of your bad thoughts every night. Let it all out. Then, the next day, reread your entries. Sometimes you will look at them and go "that was so silly, why was i so hard on myself?" but other times you'll feel all sad again, and that's when you should utilize CBT. Try to identify what's a distorted thought vs. what's a healthy one -- e.g. if something turns out badly -> your life is over, that's an example of catastrophizing. But it's ok to feel sad when you mess up at work, or disappointed when a job interview turns out badly. And you shouldn't feel guilty for that, but it's dangerous when that simple sad feeling becomes a depressed, suicidal feeling. Figure out why your distorted thoughts came about and what triggers them, and then decide how you will either healthily cope with it or fight against them.
Then of course there's the usual recovery advice like taking up a hobby and using bath bombs. I personally found focusing on my basic needs and CBT more helpful than anything, but it's up to you! Everyone has different things that they want to change. If meditating helps you more than journalling, then for sure do that instead. Just try to be realistic and gentle on yourself. You will probably be on this journey for a long time, so set reasonable expectations and don't feel bad if you fall off the wagon for a while. If you quality of life improves even a little, then that's a success, even if you aren't living the dream life you have in your head.
It's great that you're choosing this path, good luck!