Each year on the island there are two BIG carnivals and dozens of smaller ones. The two to watch out for are Las Palmas (which lasts three weeks) and Maspalomas (lasting 9 days).
Las Palmas they are still discussing. Tradition would have it start around 16th February but it looks very likely it will start 27th January, almost two weeks early. It would then finish around 19th February. What has been decided is the theme next year is "comic heroes". Expect to see lots of hunky guys in tights!
Maspalomas is the other way round, dates are decided but the theme not. It will start 25th February and finish the 4th March. The last Thursday is the Drag Queen competition which is one of the biggest nights. On the Friday there's a big street party all night and on the Saturday a HUGE street party all night long, expect tens of thousands for each of those events.
As soon as I know more about the theme for Maspalomas or the dates for Las Palmas, I'll update. You can also check Las Palmas
Offical WebSite
Official Facebook page