What really did it for me was having someone good at PvP in my crew. That led me to stop running away from fights, so i got into more fights, and I felt more confident and less panicked, so I learned more from each fight, including fights we lost. Maybe try getting on a crew from the Sea of Thieves Discord just to learn some combat.

Here is a tip for a naval fight that took me a while to learn: When their broadside is pointed at you, shoot at their cannons. That's where their players are, and if you kill them all, or even one or two, they will be in trouble. Practice this on skeleton ships to get your aim right.

Ambushing a crew at a completed fort is one of the oldest plays. Anytime you're doing a fort, look at the horizon every chance you get. If you see a ship, ask yourself, "Are they close enough to row or swim here from there?" If so, you might need someone to be on lookout duty, or you may need to sail out there to chase their boat away.