Do not clip all the way across the wing. Be careful not to clip too closely to the wing as injury could result in the event that a blood feather is clipped. Make sure you clip below the covert feathers to avoid clipping a blood feather. When the wings are clipped, the bird may still be able to fly, but altitude is stifled and allows you to catch the bird before it flies too high for you to regain control. Here is an example from African Greys written by Fran Gonzales regarding the proper clipping pattern for most birds.
Some birds are able to fly with only one primary feather.
I learned this the hard way. I had clipped one wing with the idea that it couldn't fly if it was not balanced on both sides. I had clipped 6 primary feathers on each side leaving only the outermost primary feather in tact. When I released the bird and encouraged it to fly in the house, it flew in a pattern that would have resulted in a direct collision with a ceiling fan and was not affected by the feathers I had clipped. Luckily I was able to catch the bird and remove the remaining flight feather.