Not as important a tip as wear a comfortable helmet and that fenders are very practical to add to a commuter bike, but I've had several times where my water bottle would wiggle out of its holder when I'm traveling at speed and hit a bump wrong.

I thought recently, and it seems to be working, that a couple/three rubber bands rolled down towards the bottom of the water bottle has kept my bottles more secure and that none have popped out or nearly popped out of their holder when I'm zipping down a bumpy road.

I've found, too, that having a notepad and pencil or pen comes in handy for noting places with glass or debris I want to call and notify the road crew about, or if a light won't cycle for me. This way I don't have to ride home trying to remember these notes in my head.