The "Come" cue can save your dog's life if they ever get loose. Make sure it is something they absolutely LOVE to do! Never call your dog to you and do something they don't like. It will ruin your recall. Go get them in those situations.
THe hand signal for "Come" is to bring your hand from out in front of you to your chest in a sweeping motion.
EMERGENCY RECALL: Do not use the "Come" cue off-leash until you would bet $50 they wll do it. Instead, lure them in by shaking a bag of treats. Always give the treat when they come to you.
If you have ruined the "Come" cue by calling your dog for something they hate, use a new cue such as "Here".
Tip: Keep a bag of treats by the door and give one every time you call your dog inside.
To really improve your dog's response to "Come", play ping-pong recall. Each family member takes turns calling and rewarding Fluffy, so s/he is bouncing from person to person like a ping pong ball.