Hey there,
The real trick to learning is to follow some sort of logical progression of training. Starting with step 1 is important and then the next step should be slightly more difficult than that. I can say "how not to practice" is to just randomly try different things without understanding how it relates to the end goal. No one assignment is the way to becoming a good artist. But the right assignment for where you are and what you need next is what is crucial. Is it a master copy? Maybe. Is it a dedicated perspective exercise? possibly. That is why it's hard to get good by doing assignments at random. The right assignment at the right time can literally save you YEARS of frustration.
That's why we are setting the curriculum in the order that we are. We have seen so many students try and fail due to a lack of any sensible order of how and when to try different things. I'd love to ask why not give our curriculum a shot? It will save you a lot of time and effort vs trying to go it by yourself.
However you go about it, we wish you the best of luck. : )
Cheers,
Lee