I'm not good at 1 on 1. However, I can offer a few pointers just 'cause.
1. If you don't want to have the hassle of downloading a 3D program and figuring it out, just take an item and a desk lamp. Move the light around and watch the shadows.
2. There is such a thing as reflected light. An apple on a sheet of white paper with a lamp directly over it will still have a sort of 'glow' at the bottom due to the light reflecting off of the paper.
3. Look at other art that you really like a lot. Don't copy it, but observe how the other artist does things. See if you can pick out why you like it so much. :3 In addition to this, you can watch 'speedpaint' videos online. This lets you see what the artist is drawing from start to finish.
4. It takes time. A LOT of time. Try to draw something every day or so...I'm not good at finding time anymore, but it DOES help.
5. Don't give up. Even if it looks terrible at first, keep trying. It'll get easier and easier until you start wondering how you had such a hard time in the first place. ;3
6. If you want to practice without trying to do the actual drawing, try getting free-to-color lineart and trying that out. (You can find a lot of them on DeviantArt, just search for "Free Line Art")