Chocolate Larry left a comment on how to manage stops and starts with an AC and operator aboard. The truth is that ACs just don't ride the dolly anymore (and rarely did even when we shot film). At the end of the day, it's just about control. You have to get a certain amount of mass moving in a controlled manner and also stop that mass. I use my knee a lot to get moving. Plant your foot and bury your knee into the kickpad (on Chapman dollies) or the end of the dolly. It's much easier to control a lot of weight with the bigger muscles of your legs than your arms alone. I use my knee a lot for the initial push off to get it rolling. Your arms are really just dampeners. Use them as an initial stop to start slowing down, but your body is really the brake. Larry also asks about getting marks quickly when already rolling. I'll very often find a reference such as a crack in a sidewalk or a car bumper or even a crosstie on the track as a quick reference mark. Other than that, you need to develop your sense of where the camera should be to make the shot work. That's where experience comes in because in the digital world we often roll on the first take. On the show I'm doing now we don't often even get rehearsals. We literally make up the shots on the fly (and this is a Marvel project). Here is where you need to learn the fundamentals of blocking, how to compose a frame, hold and "over" etc. Anyway, thanks for the comments!
Hope this helps!