Watch this tutorial to learn the tips how to color or shade the sketch so that it wont worst your sketch .http://www.jerrysartarama.com/art-lessons/Artists/Chuck-McLachlan/Chuck-McLachlan-Sketching-and-Drawing-Shading-and-Values.html
I don't know if this is the problem, but it helps to put your lineart over your coloring. If you're using the Flash tool, you could do that by drawing the colors and shading first, and then the lineart. If you're using the Java or CanvasDraw tools, you could do that by coloring on layers under your lineart. In the Java and CanvasDraw tools, it also helps to lock the coloring layers and shade on them.
By "Making in worse" you mean it blurs, then maybe you could outline with a pen first ( erase the pencil markings a minute or two later depending on the pen ) then make sure the pen ink is dry and color. That way it shouldn't smear.
there are tutorials on this site, although a few, and there also a lot of tutorials on deviantart. But shading correctly is mainly practice.
Also, keep the shape of the things you shade in your mind. A face isn't flat, it has curves and you should shade around those curves. Just open up your 3d program in your head and you'll have a better idea how the shadows should be applied to the face.
Shadows have multiple levels. You can nuance the differences between those levels by blurring the edges of the shadows a little bit or airbrush over it with a low opacity.
yeah... that's it >_>
Ok, so I've been getting okay at sketching pictures, but my problem is when I even shade or try to color it in it makes it worse! Can I please have some tips? Thanks!