I'm Sweetbuns, a GM. By a lovely chain of events I coach and play with a variety of players, using and learning new drills as requests and discussion come.
Drills by role
Ranged: Valla vs. Malthael matchup. Valla can perfect this if she plays superbly (from my tests around master rank). She has to have good stutter-stepping, reaction time, and the skills to focus a hero between minions all while playing around Malthael's abilities. I take this matchup to Volskaya (Sandbox) so Valla has room to maneuver and I can reset health bars and talents tiers to level 4.
Tank: Body blocking practice. You have to get that technique down! You can practice for specific scenarios as well like getting a perfect bodyblock at the choke around the shrines in D-shire.
Johanna vs. Greymane. Johanna can do quite well in this matchup by spacing out her cooldowns (assuming she has shield at 1) and focusing on the opponent instead of the wave. This playstyle applies to a lot of Johanna's lane matchups.
Reactionary interrupt practice. Learn to recognize visual and audio cues to help you react. Just pull into a sandbox match with a hero that has to be interrupted. (Easy mode is MalG, Fenix, hard mode is Muradin, Diablo and Yrel jumps). It's easy for them to take ETC here.
Assessing your tank playstyle from draft and talent tiers. Sometimes draft demands you to approach and others it has you stay back. Nail those mental habits in.
Blow-up practice. Grab a target dummy and a burst hero and show them how much followup they really need to kill a overstepping squishy. This helps them make aggressive plays and know what their DPS are capable of.
Offlane:
Sonya vs. Greymane. Close matchup. Sonya wins this if she has block at 1, plays around cocktail and applies pressure with Q while healing off wave. Good close matchup where you consider your opponents abilities.
Artanis vs. __. Really just have them practice max range swap and predicting which way you dodge if at all.
Malthael vs. Sonya (lvl 4). Malthael wins with a hit & run playstyle. Git gud.
Rexxar vs. Qhira. Bear shield for the win!
Lab and practice all them matchups. Heck throw vikings in there.
Healer: ...
Shotcalling: Predict shotcalls in high level games. Analyze draft. Think of the important talents at each tier. Generally help with mental habits and awareness.
It never ends: Position to be able to make the decisions while you're making them. Write down draft scenarios. It doesn't take long. Know the priorities and meta combinations. If both teams are even, second pick can still get a sneaky counter!
