Using a brush and ink or a felt tip marker, fill in any large dark areas that appear in your strip. Black areas help to tie the composition together.
After the ink is completely dry, go back over your cartoon and correct any mistakes. You can use a brush and opaque white to do this although, sometimes felt marker ink will bleed through, if this happens use white correction tape. You can find this at any art supply store.
To get the gray and shaded areas, use shading sheets. Cut a little larger than the area you want to shade, then, lay it where you want it to be, using a burnisher rub it against the area it is covering, using your x-acto knife, very carefully trim the excess and peel it off. You can ger the burnisher, tape and shadng sheets at most art stores. If you have trouble finding anything, please let me know and I will help.
Next: Preparing your cartoons for submission.