Draw all the things you are interested in, if you want to draw characters, draw characters, in you want to draw environments, draw environments, etc.

I know that is hard to start drawing for the sake of it because we have expectations about the outcome, unfortunately we are very aware of our skill level and because of that, we know what a "good" drawing is and what a "bad" one looks like, this basically makes us afraid of even trying to draw anything because we know that the result is not going to be good, and thus we come back to the good ol' saying "i dont know of to draw that".

Children are a good example of just simply drawing for the sake of fun without having any expectations, most children drawings suck, but they don't care, they enjoy the process and they keep drawing because for them is fun, most of them have no concept of a "bad" drawing (at least not fully) and so they are not very critical about their drawings, they just draw.

So basically, we want to achieve that "children level" with the 50% rule, we want to just simply draw the things that we want, without any single care about what the outcome is.

Now i know that this concept is incredibly hard because, again, we know what a good and a bad drawing is, but from my personal experience, once you start pushing yourself to just draw for the sake of it, without any expectations about the outcome, you will start to enjoy the process and your drawings a lot more, but you got to be patient, once you reach a certain level of conformity you will start to accept your drawings a lot more, and eventually you will start to unconsciously incorporate the concepts from drawabox and other art resources into your drawings.

So basically, if you want to draw humans and environments, you should absolutely try drawing them, even if the result is bad, try to play with it, experiment, don't let the outcome discourage you, just try to draw the things that you would draw if you had the level that you want to achieve.

Lastly, when it comes to ideas, try drawing things out of your imagination or from simple ideas at first, maybe things that you like but with a twist, you can also try drawing prompts and see how you can interpret that into a character, an environment, or a combination of both.

Also to add what LEDVI21 said, you can use reference"s", stress on the plural. For example, if I'm going to draw a Minotaur character, I would pull up some pictures of bulls, some pictures of strongman lifters, some plate armour photos, some axe photos etc. and try to mesh them together. This way you are not copying, but actively observing and creating. Although you should absolutely draw from imagination without reference and not rely on this all the time.

You are not creating an art for an exhibit, you are just messing around. Just give it a go, if you are fearing that it's going to be bad (and it will be lol), assure yourself it is going to absolutely suck, and do it anyway.