In the shortest terms ever, a cam determines how long a valve stays open and how high it lifts. More lift usually results in more hp and tq, but then you run into piston to valve clearance. More duration usually results in more hp but not necessarily tq. Higher duration also moves the powerband up, which will give you a higher peak but will sacrifice low-end. A wider LSA will move the powerband down a bit, and give you less overlap which means better emissions. A tighter LSA will move the powerband up and will increase overlap, which hurts emissions, and also gives you more "lope".

If you're going for peak numbers, look for high duration and high lift. If you off-road alot, look for something with less duration but more lift.

Whatever the case, don't over do it on the duration and lift unless you're going to clay it first to make sure you don't run into p2v clearance issues.