Hmm... I'm no teacher, but I used to do some singing a while back. Let's see what I can recall...
It helps to have a pianist. Preferrably one who can let you know when you're off key. You can cup your hand by your ear to better hear your own voice and try and get on key, as well.
Breathing is very important. One thing to practice is taking silent breaths, rather than loud ones. It sounds much better.
Hold out vowel sounds, rather than consonant sounds. You can get a much richer tone with your mouth wide open than half closed.
Also, practice exaggerating your usage of your mouth to see if you can get better enunciation. It's important to keep your sounds clear, even if it seems goofy.
Practice projecting from your chest rather than your throat. It will save your vocal cords and increase your power.
Practice falsetto (your upper register). The way I was taught was to start at your highest note and sound like you're falling off a building. We would do those exercises before chorus class every day.
And of course, practice practice practice. Learn the nuances of the songs you're singing. Once you get the technical aspects of them, work on feeling the songs. Make sure you know the words. Etc. Etc.
...Then again, this is me remembering classes and clubs from 5 or 6 years ago...
Pereant qui ante nos nostra dixerunt.
