I sing reasonably well. My claim to fame is one year of voice lessons (opera) and I play flute (breath control principles are identical).
My advice (to be taken with a grain of salt): Scales are your key to vocal control. They're the most efficient way to gain control and improve. Get a piano/keyboard/guitar and sing scales while playing along. This will help you hear whether or not you are in tune.
- Sing scales slowly without vibratto to practice things like breath control, beauty of tone, and intonation
- Sing scales fast for agility (be careful to stay in tune)
- Sing scales in thirds (do, mi, re, fa, etc.) and other intervals
Stuff to watch out for:
1) RELAX!!! You can't sing with a tight throat. You want to feel like you're yawning, not squeezing.
2) When you're tired, you will probably go flat. Being flat sounds worse than being sharp, so try to be sharp when you're tired. (in case you don't know: when discussing errors of intonation, "sharp" = pitch slightly higher than it should be. "flat" = pitch slightly lower)
3) Learn to breathe. If you're breathing into your upper chest and raising your shoulders, you're probably doing it wrong. Use your diaphragm. To find out how, lie down on the floor and take a deep breath. Your lower belly should expand. When you forcefully exhale, your lower belly should feel like it's trying to expand (abs are engaged). I hope that made sense...
4) Always start with a warm up. Your voice is a muscle. If you don't stretch it, your chances of damaging it are much higher. You can stretch your chords by warming up with scales.
I STRONGLY recommend taking 3 or 4 voice lessons if you're serious about singing... just so you can get the basics down. Happy singing to you!