To bid well, you must estimate whether a card will take a trick or not. A 18 or 20 is very likely to take one, while holding a 5 or 8 would make that nearly impossible. Bid 1 for each card larger than 17 is a good idea, but pay attention to the fool who can make your low cards taking a trick or making a high card loses a trick!
The fool (or excuse) is a card that can be 0 or 22. When you bid, it is offen a good idea not to count the fool as a trick. This is because if you fails to take a trick that you attempts to take, the fool can fix the mistake.
It is always a good thing to play last since you can see all the other cards played.