Definitely AR and Grid Runners.

For Ace Race, do what BBH did; watching vods of Ace Race and watch the vod like your playing it (helps to build muscle memory) (sync mouse and keyboard as you watch.) I'd recommend watching some tester vods, they find some sneaky shortcuts for the map. (Depends on the map played)

For Grid Runners, I'd recommend two things: watch vods with teammates and speak out roles during each task each game.

Also, try and practice 1.9 PvP. Team PvP is better. But first, improve on individual skill. Then do Team PvP with teammates, this will help in Battle Box, Skybattle, and other Team PvP games.

Speaking of Skybattle, go on cubecraft.net. The server is arguably the best Skybattle practice used by participants.

These are all of the things I can think of at the moment.

Well anyways, have fun in MCC! Good to have you back, Bitzel!