IMO, the biggest time saver is going to be making a Rollable Table out of whatever version of the Hit Location Chart you're going to be using. It can get pretty finicky if you're using all the expanded locations from Martial Arts, but 20 minutes of work beforehand saves a lot of time during the game. A close second is working on a mega-macro for attacks that rolls the attacker's 3d6 roll, the defender's 3d6 roll, the weapon damage and then the hit location macro described above. Sure, sometimes most of that macro won't matter, but it saves you telling people what to roll next or forgetting to roll someone's dodge/parry attempt. It never hurts to have a plain ol' [[3d6]] macro for everyone too. As a mentor you can automate quite a bit via the API, but I prefer keeping as much as possible external to Roll20. So, we used Gurps Character Sheet uploaded to a folder on Google drive rather than having a million attributes that could change. YMMV on this part, obviously.