Clipping a bird's wing requires very sharp scissors (smaller size may be best.) Hold the bird securely but gently, taking care not to close your hand over the bird's chest (this will prevent breathing and bird will panic.) Clip the grown-out primary feathers back until they meet the edge of the secondary feathers. This will yield a neat, blunt clip. Optional clip is to leave the first two primaries - marked here as "A" and "B" - to give a visually full looking wing. DO NOT LEAVE outer primaries on strong fliers, i.e. cockatiels.

Facts about Clipping Birds' Wings 
Clipping a bird's wings is safe and painless when done correctly. If you do not know how to do it yourself, find a pet shop that specializes in birds and have them do it for you. Often a bird will resent being handled during wing clips, and having it done by another person allows the bird to feel any ill-will towards the bird-groomer and not you.

Birds CAN FLY with clipped wings...a clipped bird IS NOT ESCAPE PROOF! They are slowed down, and they fly lower and clumsier, but are still potential victims to household hazards: open windows or doors, and other animals. Watch for clipped feathers to molt out...new feather re-growth can happen very fast, creating a wing with full-flight capabilities. NEVER CLIP A PIN-FEATHER! (see "C") This opens up the vein and the bird can bleed to death. Wait until the feather is all the way grown in, opened and hardened. While your bird is growing new flight feathers; and they have an active blood supply; restrict time out of the cage.