Agree 100% with what the other posters have said. The only caveat I would add is to make sure that the spring loaded arm that extends and holds the front wheel of the bike is secure. With all the abuse these racks take, sometimes the spring breaks or there is a lot of play in the rack. I've only had one instance where my bike was damaged by the rack and that was when I used a rack with an arm that had a lot of play. The driver had to stop suddenly to avoid a car that had cut her off and the bike kind of pitched forward in the rack, causing the rim to bend. It may have happened if the rack was perfect anyway, but the fact that the bike almost flew off and was leaning outward at a 45 deg. angle certainly didn't help.

Like everyone else, I remove panniers, water bottles, cyclocomputer, etc. from the bike before I load it onto the rack. Once on, (and if the rack is in good shape), they are very secure.