Treat your lyrics like lines in a play. Most songs have a message, and it's your job to get this message across to the audience. If you're singing in another language, translate the song word by word so you know exactly what you're singing about. Think about who is narrating the song, and imagine that you are that character.
Command the stage with your presence. When you are onstage, the audience should be paying attention to you -- and you should act as if you expect that from the minute you walk on. Be confident: stand straight with your shoulders back, and take up as much physical space as you can. The whole stage is yours, and you should use it.
Talk to your audience. Just a few words of greeting before you start a song can lighten the mood and create a connection between you and your audience members.
Make eye contact. You don't have to stare at people, but give the audience the impression that you know they are there. Many performers choose to ignore the audience, but you will have a better rapport with your audience if you acknowledge them with a look.
Acknowledge the audience. A simple "thank you" when they applaud will improve your relationship with the audience. If an audience member does or says something unexpected, turn it into a joke instead of ignoring it.
Smile. No one wants to watch a singer who isn't enjoying herself. The only time it's okay to stop smiling is if you're performing a very serious song.