I have been to the Maldives and done some snorkelling, firstly, get a mask that fits, properly, once this is in place it will make the snorkelling a lot more fun and if it is anything like Meeru there will be a chance to go out onto a reef via a boat, these are equipped with bouyancy aids, then decent fins are very useful, I went to decathlon and tried loads on and settled on some mares fins that and a breathing tube to complement the mask and I wasted about 7 of the 10 days with my head under water, the shoes are usefull as the beaches are made up of broken coral, a little coarse in places
You will have a great time