as stated above, do not stay in Belize City - get to Ambergris Caye (pronounced Key) via water taxi/boat (cheap) or Maya Airlines (costs more than boat but way faster and more comfortable
We did AirBNB here -
https://www.airbnb.com/rooms/13223486 it's very near Ramon's which is awesome if you want a nicer hotel type place. Ask for Tony - he'll help you set up everthing and also pick you up in his golf cart when you get there.
Day 1 -arrive and just settle in, grab dinner at Bluewater Grill (contact Norma and meet her this evening to set up Days 2 and 3)
Days 2 and 3- snorkel adventure and Maya Ruins - consider Belize Diamond Adventures - ask for Norma - she can set you up for a Snorkel Adventure as well as a Mayan Tour (Cave Tubing and Zip Line is good as well as the Mayan Ruins)
Grab coffee / quick breakfast at Island Buzz each day
If you skip snorkel or Maya Ruins (I'd skip Mayan ruins) then spend a day at Secret Beach - get there early and take pictures - amazing water!
Dinner a Carambas, Elvi's, The Truck Stop, were nice
WiFi is in all restaurants so don't worry about not having cellular connection
hope this helps! let me know if you have questions