I bought a tripod recently and so I have a few pointers. These are the things I looked for in a tripod, in order of importance.
1) Is it the right height? No point buying a Manfrotto if it's the wrong height and doesn't do what you need it to do.
2) Does it support your camera's weight? A DSLR with a zoom lens is a very heavy piece of equipment.
3) Does it have the right compromise between being sturdy and lightweight? You are going to be lugging that tripod around, so you need something that's light. Equally, you don't want it to be so light that it doesn't adequately support your camera.
4) Does it break the bank/ruin marital harmony/etc? My wife would have killed me if I got a Manfrotto
5) Other random niceness to have: carrying handle, level indicator, detachable head are nice things to have but you might be able to live without them.