I just picked up the game and played one course, and my putting is stellar, thanks to Mario Golf GBC. Here are a few tips I can give you which will definitely improve your putting right away;
1) This is the most important. If your putt is less than 30 feet, then all you have to do is set the power of your shot to be 4-5 feet more than the distance. So if your ball is 16 feet away from the hole, and there aren't any slopes or hills on the green, just hit it at 20-21 feet power. It will go in. The only time I wouldn't do this is if your putt is within 5 feet of the pin. Unless it's raining, all you have to do then is just hit it 1 or 2 feet harder.
2) If your put is more than 30 feet away, then it gets trickier. If it's 30-40 feet away, hit it +5 feet harder. Unless it's like 60 feet away, you usually don't want to hit it more than +10 feet harder.
3) When it rains, the green slows to a crawl. So if you're putting, and you're +16 feet away from the hole, I'd hit it about 24, 25 feet. With rain, you really just have to get a feel for how hard you should hit it, as it's really difficult even for me to estimate sometimes.
4) There is a difference between having the hill slope to the left right near the hole and having the hill slope to the left right near your ball. Think of it like this:
If you're hitting your ball and the hole is 20 feet away, what happens? You hit your ball, it goes fast, and then goes slower as it nears the hole. If the slope is right in front of your ball, then it won't affect your ball that much, as your ball is going fast thanks to you just hitting it.
However, if the slope is near the hole, then it's going to affect your ball a lot more, as your ball is going slower. Your ball is going to touch the slope for .5 seconds if it's right in front of your ball, but it will touch the slope for 3-4 seconds if it's right near the hole.
5) With that in mind, lets say you have a long putt, say 30 feet. The green slopes to the left in front of your ball, goes flat, and then slopes to the right in front of the pin. For the sake of the demonstration, lets say both parts of the green slope at the exact same amount (ie neither slope is steeper than the other).
So it slopes left, is flat, then slopes right. Are you going to want to aim left, straight, or right?
In some cases you'll just want to hit it straight, as long as there's not much of a slope, but in most others, you'll want to hit it left. Why? As I went over, when you hit the ball, it's going to speed over that initial left slope part, and the ball's path won't greatly be affected. But when it reaches that right slope before the hole, the ball will be going slower, so it'll curve much more.
So instead of seeing two slopes that should cancel each other out, you've got to take into account how fast your ball will be going. The ideal shot should look like you're aiming a little too much left. Right after you hit it, it'll move even a little more left. But once it reaches that right slope, it'll curve right into the hole.
So yeah, those are the basics. Hope that helps.
