You should plan your trip to the Seychelles around what you want to do

Windsurfing and sailing are best at the start and end of the trade winds, usually around May and October. Some beaches are better during the monsoon season, others during the trade winds. Diving is best in March to May and September to November. Hotel prices shoot up and accommodation can be hard to find during the peak seasons from December to January and July to August. Easter can also get busy.
There are more shades of blue and green in the Seychelles than it is possible to imagine. Forming a backdrop to the relaxed tropical image of the Seychelles are the rhythms, colors and flavors of Africa and gris gris, the local brand of black magic.