Paraphrase to show you're listening
Part of being a good listener is actually listening to what others have to say. You will come off as sincere and genuine when you listen to a person if you can paraphrase what they said back to them in agreement. However, don't take it too far and repeat everything they've said verbatim, find a balance.
When you want someone's help
If you need assistance doing something, start by telling the person, "I need your help." This will make it seem like you really need them, making them feel guilty when they contemplate not helping you.
If you think someone is watching you
When you can't shake the feeling that someone is watching you, do your best to let out a legitimate yawn. If you can yawn and look around a bit, the person watching you will likely yawn as well due to how contagious this behavior is.