Well I'm still developing myself so it's probably best not to take everything
ultra serious.
I think sai might be a valid way of practising on its own. Mostly because there's no need for commitment with a digital canvas. It does take some time to get used to but eventually you'll have some way of scribbling whatever with no real need for commitment. You doodle a bunch of stuff on paper, you have to get another paper and so on, with a digital canvas you just erase it and pick back up immediately. So it might be easier to pick that up and try making a bunch of arms or something.
Second, again another thing I do with sai,
studies. Get a bunch of images of things you wanna learn and draw next to them. And then keep doing that with whatever you feel you need to change. Here's a little example from myself
Going from left to right on the top row and right to left on the bottom, you can see that while I do have some ways to go, I'm still getting a better understanding of how these faces work. Also finding stuff to compare tricky subjects to (in this case, a gorilla's skull) can help immensely too.
Also, even when you're not drawing, just keep art in mind at almost all times. Think about how random things you find are structured, look up refs and guides, all that stuff. Even when you're not exactly drawing you can still learn.
Like I said, I think some of this may need a pinch of salt but that's how I'm going about things.