Rather than thinking about how to improve your drafting ability, you should focus on improving yourself as dota player first because drafting ability comes with your understanding of dota. Generally this should be your guideline, understand why they're strong. Then ask your players to practice the heroes on the list.

Last weekend my team participated in amateur tournament, 3 permanent members + 2 standins. Literally every game we had different standins, we just picked anyone who were free to play from our friendlist. We managed to get fourth place from 45++ participating teams. We could have done better if we managed to get decent standins for the semis.

I drafted for my team during the whole tournament, except during the second day when i woke up late and missed 2 match. 80% of my picks/bans were on green/blue tier from the list that i linked above. Its not like i memorized the list btw, i kinda know about whats strong/weak in the current meta.

This is how i train my support. I told him to play only razor and void in solo rmm. Sometimes when we train together as 2 stack, i will ask him to go carry. Good support must understand how carry thinks.