I was having trouble sketching for my lastest WIP, King Pong, and a simple sketching trick helped me out. I was struggling with the size of each part of the sketch maintaining what I was sketching from.
First, get a ruler and create a grid of squares over what you are sketching from. Then make a grid, larger if necessary, on the paper you will be sketching on. This allows you to have smaller frames of reference for each piece of the sketch and makes increasing the size of the object a lot easier. Note the difference in size in the following sketch:
(you can click the images for larger versions)
Second, once your sketch is satisfactory, go over just the sketch not the grid with ink.
Third, get yourself a nice eraser, and once the ink is dry, erase your sketched grid.
Fourth, scan your image, make it black and white, up the contrast once or twice, and if you have Illustrator, do a live trace. I did a live trace, and then printed it out because sometimes on certain spots the ink is too weak and it needs to be re-inked so you can re-scan the image and get a better live trace.
Finally, add color.