High season is November through April, but if you don't mind afternoon rain showers and a lot of humidity, late June through October is a great time to visit for lower-priced lodgings (up to 40%) and rental cars and smaller crowds.
By August the entire coast and inland forests are green and bursting with blooms. Afternoon rains clean the streets and houses; waterfalls and rivers outside of town spring into action. On the downside, many restaurants and some other businesses close shop in the hottest months, August and September, and performances and nightlife slack off.
Overbooking is a common practice. To protect yourself, get a confirmation in writing, via fax or e-mail.