However, it's not always a bad thing for your fingers to be touching strings you're not playing. Sure, play with the tips of your fingers, but as you develop in skill and try to play more difficult songs, you'll find that they require you to muffle the other strings so that you don't get unwanted noise.
Of course, if we're talking about trying to hold chords and they don't sound good, well, that's just gonna take practice. Some good things to keep in mind are:
1. Most of the time your thumb should be at the back of the neck rather than looped over the top of it. Point it roughly towards the ceiling, too.
2. Don't cradle the guitar with your left hand. The guitar should be supported by your leg, your right forearm, the guitar strap--anything but the left hand.
3. If you have to look at what you're doing, tilt the guitar to form the chord or whatever and then tilt it back so that you can't see the fretboard. So many people twist the guitar back to see what's happening, but in doing so you create more stress on your wrist, because it gets bent back further.
Have fun. :)