Setting up in a doorframe helps a lot, and don't reach out with your hand to stabilize - use your shoulder/elbow to 'bounce' off the wall if you need to correct your path. Reaching out with one hand makes things a lot harder for beginners - it's essentially riding rollers one handed and worse since you tend to put weight onto that reaching hand which screws up your balance. With a bit of practice, you'll be able to ride your rollers blind, just with very gentle taps on the walls if you veer left or right.

My favorite and honestly, only useful move that I've acquired on the rollers - looking back over your shoulder to check for cars while holding the line. If you've never done this, you're in for a rude awakening on rollers when you discover that you veer a lot off the line when you do it. Once you get good at it on rollers (doesn't take long at all), you'll be able to ride on the rollers looking straight backwards for minutes (I do 1-2 minute holds looking back) if you're in the doorframe, without even looking forward. (Again, bump off the doorrame to correct mild lateral movements.) Makes doing this on the road orders of magnitude safer, evne in fast and tight groups.