Definitely dodge objects if you are able. If it takes a severe maneuver and you might crash into something or weave into traffic, it may be preferable to brake hard and hope for the best. When going over an obstacle-- big bump, hole, etc-- you will want to 'get light'.
Raise yourself off the seat at least an inch and try to let your arms and legs act as shock absorbers for your body weight. You don't necessarily need to fully stand unless it's a really big bump, we're talking jumping curbs. (Which I don't recommend.) Usually just raising yourself a little is enough... make sure to practice this skill as you don't want to be unbalanced because you never stand up.