If you're from America, before you go, you gotta take your fast paced life and put it on pause...everything in Anitgua is on Island time. So be prepared for all the service to be s l o w.
Now that you've been warned, enjoy the the island. The most beautiful beaches I have ever seen are here. You must get a rental car! So arrange it before hand, otherwise you'll be screwed over by the airport rental car agents. But another tip, the roads are so underdeveloped. No signs outside of downtown, no lights, many many potholes. It is quite an adventure. You should get a map of the small country and follow the road paths marked. It's kinda like on a treasure hunt. Driving is dangerous but it's the best way to get the most out of the island. Taxis are very expensive.
Anyhow, we got the most out the island by renting the car and following the recommended driving tour in the Antigua visitor magazine. You must visit Devil's Bridge oh and Half Moon Bay.
Food wise, the BEST restaurant on the island is called OJ's. You can get a whole fish with sides for $13 and it is so good. Even the tuna! I believe it was like $6 and it was the best tuna I've ever had in my life. It's near the Rex Blue Heron hotel on the south western part of the island in Johnson's Point.
Don't waste your time at the big resorts. There's so much more to see. My favorite beach has to be Turner's Beach right by the Blue Heron hotel. Half Moon Bay acutally had waves so that was fun (that's on the eastern side).
Try the coconut ice cream. And buy some guinnips from the street people downtown.
The best nightlife is in English Harbor. There's an Italian place that has really good food, but I can't remember the name.
Oh yeah, and don't forget to bring BUG SPRAY! We were eaten alive by the sand bugs/mosquitos.
If you wanna be ripped off, stay near the big resorts (clubs, restaurants, etc).
Take the Adventure Antigua tour. It was phenomenal. Small groups. You go snorkeling, hiking, and get to walk over Hell's Gate. Bring sun block.
This is a great, little secret of the Carribean. In about one week, you can do just about everything on the island.