Hi!
Well if you're looking for advice right here and right now instead of going out and looking for books or teachers, this may help.
The first thing that my teacher always tell me is the the breathing and support of your singing is always key because it is the backbone of your singing. So before you sing anything I would do some really good breathing exercises and make sure you're breathing correctly and with good support throughout your singing, and not just when you're warming up.
Second thing I would do is try to see what your range is just because I feel like that's important. Just go to a piano and play a single note, match it with your voice, and see where on the piano, high and low, you cannot sing any higher or lower. This will give you a good idea of your current abilities and maybe your goals for the future.
Then I would focus on hitting notes and tuning dead on so you're not pitchy and all over the place. You basically have to train your ear which is difficult but all you have to do is just take the piano and practice playing notes, riffs, and melodies on the piano, easy and hard ones, and make sure you hit all of the notes. If the note sounds right to your ears, get a tuner and check because your ears may not be right.
Other than that all I can tell you is to really get a teacher or a book or something official to help you. Also, focus on the breathing that I was talking about because with proper breathing and support at all times, you will be more in tune, will be able to hit higher and lower notes, and your tone will be better.
I really hope that I helped in some way!
Mary