I pull it taut when putting on trim. I do this for thin and thicker strips of trim. It always seems to pull out the problems before they happen.

When going around curves like canopies, you have to pull it tight. I go around the shapes with a length of covering that is about 6-12" from my fingers and the surface. This gives good pull and movement to follow the curves. The thing to remember about curves is that you have a tightening of the covering on the inside of the curve, and stretching on the outside part of the covering. I pull hard and tamp down the insides as I go around. The outside will lay well if you get it right. The pucker problems are when you have too much material on the inside of the curve.