Need help using canon

Practice on npc ships like skellies and Phantoms instead:

Phantoms will have you with your aim while moving since it doesn't matter where you hit them.

Skelly ships will get you used to compensating for wave heights.

practice is definitely the right idea, it's almost entirely muscle memory and you'll notice yourself get much better with time. depending on how close you are to the inactive fort when practicing you could be reducing waves. waves are significantly reduced near islands so you're practicing in different conditions than you'll be fighting in. try to aim at stuff while sailing at a reasonable speed away from islands.
one tip that may not be in most cannon videos is that waves are always the worst when you are sailing northwest. if you get the choice try to take a broadside when they're going northwest and you are not.

@Bryant-siew As a general tip, if a ship is very close, aim lower than you think, and far away, aim higher than you think, everyone always overshoots close ships and undershoots distant ones, but the best thing you can do is just practice, it took me quite some time to get used to gauging where to aim on a moving ship if its faster or slower, but with time i got better, and i know anyone else can!

As a tip for the future when you get better with cannons (or if you have since the time of posting) blunder bombs arnt just your ally in ship defense, if you down some ones mast, it helps keep them from repairing, and if you down a player, blunder bombs help prevent a res and can even kill the person who is trying to res.