I did mine myself as well. I bought my house new, so I didn't have the unfortunate job of removing oil/grease stains, etc.
If you do it yourself, make sure you degrease and get up any stains you have as best as you can, etch the concrete, then let it dry. Make sure the concrete is completely dry before you roll on any pant or epoxy, otherwise you risk the paint/epoxy bubbling later. You can tape down plastic sheeting and leave it for about 24 hours, then check to see if any moisture has built up on the plastic. If so, there's still moisture in the concrete that needs to evaporate first. If the plastic is dry, you are ready to roll on the finish.