Before you try figuring out how to draw letters and numbers distinctly, figure out which letter/number pairs are giving you trouble. Some differences between letters, like the difference between the large and small C, S, and Z, are not easy to do differently, as they are the same letter only different sizes.
Here are some examples of things I've seen people do to distinguish glyph forms:
1, you can opt to draw serifs on the
1 (like they have in the monospace font: compare I and
l as the only straight line.
Z, you can draw the
2 with a loop (like a cursive Q) or put a line through the
S, some people put the upper bar of the 5 a bit lower. (It's mostly people from Asian countries that do this, in my experience. )
q, you can draw a hook or loop on the
q (This one might not apply to you; but I draw my 9's and q's the same way.)
Drawing a bar on the 7 is only necessary if you normally draw 1 the way it appears in this font, instead of with the bottom bar like this:
As DA01 said, if you need the letter forms to be recognizable without any context, then it's not a good idea to use symbols that are indistinguishable from each other or that could potentially be confused (for example, the Magic the Gathering rulebook does not use "l" or "o" for letter sections because they could be confused for 1 and 0).