Study the facial gestures and posture of popular singers. Singers have a distinctive style and you can emulate your favorites.
Learn the words to the songs you want to fake sing. Knowing the words makes your fake singing, or lip syncing, seem more realistic.
Listen to the songs over and over. The song has to be familiar for you to fake sing it correctly. Memorizing a song's breaks and rests is very important to a good performance.
Watch yourself in the mirror. This is one way to get a true understanding of how you look when you fake sing.
Videotape yourself fake singing. Watching your fake singing act may make you cringe, but be realistic and learn from it.
Give a fake singing performance for friends or if you're really brave step on stage at a local amateur night and fake sing your heart out.