Type in “Figure drawing excersices” on google. There are several sites (you can learn after one or two uses which one you like the most) that give you the excersise.
If you’ve never done it: It’s a series of photos, each on is on screen for 20 seconds to a minute (you can set it). The idea is that you sketch from bigger to smaller: First lines of direction, then general anatomy, then blocky anatomy, you just add more detail until the pic changes. Then you can go back and correct them after the excersice is over.
No matter what style you want to draw in, getting better at copying and understanding reality will help you improve. Realistic anatomy is a must. Realistic perpective is a must. You’ll bend the rules however you want, but first you gotta have a good grasp on them!