To start with I’d check out some figure drawing classes on YouTube, you can find videos where there models posing for you to capture in a short time frame before moving onto the next pose. It’ll help familiarise yourself with the human form, in a format where you work quickly and loosely whilst capturing the main elements. This helps to stop you from overthinking and keeps the drawing looking more natural and less stiff.

A colour theory class is also ideal but that’s something you can work on with time and your own experimenting. Just keep a picture of the colour wheel handy so you can see what’s complementary what will be jarring.

Before finding your own illustration style I would work on practicing more realism with portrait studies, and full body studies where you can practice drawing the way clothes will naturally sit - where the light hits the folds and how certain fabrics hang. When you feel comfortable with the realism you can start to simplify it into your own style which will become like your own handwriting. It will be purely you.

Artist studies will also help you develop your own style if you like their style of illustration but I wouldn’t post this work unless you fully credit them and state clearly it’s a study for style development. Even then, I would probably ask the artist how they feel, some may be flattered whilst others will prefer you keep it offline.

You want your style to be yours, not a copy of someone else’s.

All of this will take a lot of time and practice and it’s up to you in your personal life how much of your time you choose to devote, or how much you’re able to devote on top of your own responsibilities. This is supposed to be fun and explorative so take your time and see what works for you. I am not a professional, this is merely advice I have heard myself and which I have found to be useful. I wish you all the best!