Let's see...
#1. Sailing
When sailing, there's the normal way to get around by going in the exact direction of the wind, but there's other ways of getting around.
When traveling short distances (like to get to a Fishman [who will fill out your map] or back to the island in the square after you've gotten the fishman) instead of playing the Wind's Requiem (changes the direction of the wind) you can zig zag against the wind to get to it. For instance, if the wind's blowing north at the time, you can zig zag between east and west until you're at the island. I don't recommend it for long distances though.
And then there's my final tip for sailing. Firstly, sail with the wind directly behind you and keep pressing toggling like mad between having the sail up and not having the sail up (so as an example, based off my preference for having the sail on Y, it would be Y,A,Y,A,Y,A,Y,A,Y,A,Y,A,Y,A and so on). It may not seem like much, but it'll probably help you with keeping your mind off the whole thing that the boat moves slow and also keep you at top speed, letting you reach your destination faster.
#2. Dungeons
In dungeons, always make sure to open up the Warp Pots. They're very useful since in every dungeon, there's a Treasure Chest with a Treasure Chart that is near the beginning of the dungeon so that's good for 100% completion.
Always look around and try every item you have on something you think is suspicious. See a cloud of gas and no progression in either of the rooms to the side? Try everything, from your Deku Leaf to Medli herself (it'll make sense once you get to the fifth dungeon).
#3. Try Everything
Try everything that's available to you. From the Battleship Mini Game on Windfall to the Bird Man contest east of Dragon Roost, try out every mini game you can find. You never know what you might get, be it a Piece of Heart, a Treasure Chart, or Rupees.
#4. Get the Upgrades as Soon as possible
Okay, so the Wallet upgrades in WW are extremely important. Not getting them early enough can mean monotonous rupee grinding and that's no fun. So, get the Wallet Upgrades as soon as possible. I won't tell you exactly where they are, but a certain Chart can. Simply rescue Tingle from his prison on Windfall (simply go in the door closest to the guy dancing at the tombstone [pizza]) and he'll give you a chart that tells you exactly what island the Wallet Upgrades are located on. Good luck with the second one.
Which brings me to my next tip...
#5. Never Pass Up a Rupee
Simple as that. Never pass up a rupee. A single green rupee may not seem like you're missing much, but they are very important. If it's in a pit of death, don't worry about it but don't scoff at the chump change either. Simply pick up as many dropped rupees as possible and a certain part of the game will become much easier.
#6. Explore Everywhere
This goes double for the overworld, where there's tons of stuff to find. There are Treasure Charts, Ammo Upgrades, Hidden Rupees, Heart Pieces, Charts, etc. etc. So, make sure to explore every square thouroughly. See a hole? Go down it. A bunch of cannons and bomb ships? Shoot them all down. Hookshot target? Hookshot to it. Bunch of switches? Hit them all. A submarine? Enter it. And so on and so forth. Also, a bit of advice for the platforms (you'll know one when you see one, they're extremely hard to miss). On most of them are cannons. You can shoot them from your ship, but placing bombs above them on the platforms can destroy them too.
And that's it for my advice. Remember those six tips and you'll be on your way to beating it 100% in no time.