if you REALLY want to get good at a semi realistic style, id start with doing 1 minute gesture drawings, its in my opinion the most important thing for making dynamic looking poses. practice them every day as a warm up and if you are up for it id recommend try to do at least 30-60 1 minute gesture drawings everyday for as long as you can, even professionals still do them after decades of learning.
next id work on value, which is another thing i believe is crucial to creating believable drawings. Values are even more important than colours, you can technically randomise all the colours in your drawing and as long as the values are good the forms will still read.
Drawing lots of 3d shapes will also help alot with constructing forms. id recommend learning the very basics of perspective, like how to draw cubes in perspective, and practive stacking them and moving them around in space.
imo if you wanna really kick start the learning process id go for a daily routine of something like 10 minutes of 3d shape drawings(drawing cubes/cylinders/cones in perspective and stacking them on each other and things like that) do 30 1 minute gesture drawings(you can use a website like https://www.sketchdaily.net/ and set it to 1 minute.) then do some value studies(they can be of things like cubes and stuff with lighting, or if your up to it a grey scale portrait study)