I am glad you asked, as most people just assume they know how. Cutting the end of the tube at 45¡, as recommended by most caulking manufacturers, is not the best idea. It is better to cut it straight across. A tube cut at 45¡ will produce a nice looking bead, but it will not force the caulking hard enough into the crack. Also, laying the bead gently on the surface won't help it to stick. You should hold the caulking gun perpendicular to the surface to be caulked so the compound is forced into place as you move the gun along. When filling a hole, you should put a backer rod into the bottom of the hole so that the caulking can be forced into the crack and pushed up against both sides. A caulking bead should not be more than 9 mm (3/8 in.) thick and 12 mm (1/2 in.) wide. If you are caulking a hairline crack in a concrete wall, chisel out a groove of this size right over the crack. Don't simply fill the crack with caulking; if it sticks to both sides and the bottom it will have no stretching ability if the crack moves again. The trick is to put masking tape into the bottom of the groove, covering up the crack, then caulk. The caulking will stick to the two sides of the groove but not to the bottom. If the crack moves again, you have a full 12 mm (1/2 in.) of material available for stretching.