How do you get goalie gloves to get less slippery?

With Keeper gloves (If they have a latex component) you can wet them by placing a small amount of water on them or you can spit saliva on them. This softens the latex slightly giving them a stickier surface.

Some Goalies have in the past used spray glue (Upholstery glue) on the palms before a big game, but keep in mind the solvent in the glue usually degrades the glove much quicker.