Keep it simple!
Have party last 2 - 3 hours maximum.
Eat sweets in last half hour
Have back up indoor activities planned if having an outdoor party
Letting kids do a craft as you wait for everyone to arrive keeps things organized.
Pick a theme and run with it.
Google for ideas, invites, recipes, and everything thing else on the internet
Give your camera to someone else to take pictures, you may be to busy to remember the important shots
Have another adult (or older child) to help you if needed