A challenging game - I believe it to be meant to frustrate you over and over as I've died everyway imaginable although am now at day 15 on my latest attempt. There isn't specific tactics to survive although it's suggested to get your Tent, water reservoir and fire pit set up so that you can at least stay hydrated and fed.
SAVE AS MUCH AS POSSIBLE
If you plan on exploring the islands, do it one-by-one and bring materials to build yourself a tent on the new island. DO NOT LOSE YOUR RAFT: if you do, you will have to build up your strength so you can swim back to your initial island and this could take a couple in-game days .