nameste - You will have a great time. Of all the places I have traveled, alone or not, Belize has been the most comfortable. The fact that everyone speaks English is good for me as my Spanish sucks. The exchange rate is simple. And like Jackie says - you will meet all sorts of interesting people.
The common sense things are just what you would normally do (and NOT do) anywhere.
How long are you staying? Are you planning on staying in AC only?
Be sure to post your adventures when you get back.
And take lots of pictures.
laugh