1. If you happen to travel through the same airport often,get a few copies of the customs forms and fill them out in advance, in order not to delay your lineup.
2. If you have a way to fast-track customs, do so. In Canada we haveCanpass which will make your trip through Canadian customs much faster, as you get to bypass the regular lineup. There is another program called Nexus, which is currently being trialled at Vancouver airport. Nexus is a joint program between Canadian and US customs authorities to allow travellers from either country to fast-track.
3. If you are flying on a short trip, do not check any luggage.
My friend uses Canpass and loves it. He says that he now avoids the big lineup at customs, and that he does not get stopped any more than usual. I am going to try it out and let you know what I think…