Crash is the first boss you will run into as you pursue the story. You will have fight him in 2 different phases. His ship phase is the harder of the two. There's a pattern to it though that certainly helps quite a bit. He switches between shooting with his cannon and then burst firing with his turret. I would recommend backing up a little and just focusing on dodging when he is shooting with the turret. Most of your weapons won't reach the boss from far back and it's easy to take a lot of damage when close to him. When the boss is shooting his cannons is where I mostly focused on shooting. There is normally little gaps in between his cannonball fire that you can just sit in and shoot. You have to break off armor parts before you can do any real damage. After you break some of those parts off there are some critical components that will deal massive amounts of damage once broken. I tended to focus on breaking the engine at the bottom of the ship.
Once you break his ship he will regenerate half of his health and you will have to fight him again in his human phase. It is quite easy, the hard part will be if you used all your ammo and health trying to break his ship form. you can break some boxes near the edge of the island and it usually drops a health pack which helped me a ton. Just dodge through his bullets and you should be fine. His human phase really is quite easy.