I've been playing guitar and singing for a few years. I'm not professionally trained, but I know my range and I have fairly good control over my voice. My voice has improved significantly each year I have been singing. Listening back to old recordings, a big problem I had was that I was singing through my nose. Make sure your posture is straight and try your best to breathe in and out through your mouth and nose. Also, make sure you're breathing through your diaphragm and not your chest. Once you get the breathing part down, play the song you want to learn to sing and try your best to sing along. Of course, once you get better, you'll find your own style, etc. but try and sing along the best you can. That's all the advice I could really give with my knowledge. Good luck!