Our best advice is to focus on making a simple grill, simple purifier, fishing rod, and spear as your first items. Remember that water and food are essential items to stay alive in the game and it's a good idea to have a spear to defend yourself against the dangerous threats of the sea!
If you are having a rough time you can also try different game modes. If you are having a hard time with thirst/hunger you could try easy instead of normal, if you think the shark is anoying you could try peaceful. How the game modes differ is explained when choosing the game mode when creating a new world.
If you aren't sure on how to start out, there are a lot of guides and videos out there that can help.