I need tips

My advice to you would be to take a simple ball and set it under a lamp light. Draw the pic with the light source. Keep doing different angles with the light source. It will help get a better understanding of how a shadow truly falls and shades into the darker area. I hope you find this helpful.

I hate to respond to this without any actual help to give you but you could always try sking around on art websites for advice. I'm a member at Deviantart and I get lots of good feedback and advice for photography there. People post drawings and there are a lot of talented people there to get some advice from. You could do some of the forums too. There is another website called ArtWanted, but I think it's more for selling your work than getting feedback. RedBubble and Viewbug(more for photography, but I'm sure they have people who draw also) are other art sites you could try.