I organize first by type (spices that will be used in baked goods and sweet things, like cinnamon, nutmeg, cloves, etc., and spices that will be used in savory dishes (garlic, cumin, etc.). Then, I like to have my most-used spices in front. For example, there is an herb-garlic grinder (Spice Island or McCormick) that I use every day. I put it in soup, chili, pasta, rice, salads, etc. so I like that to be in the front so I don't have to look for it. I use cinnamon a lot so it's in front also. Occasionally, my husband will rearrange the spices by some other method, perhaps by sizes, tall in the back and short in the front. I complain and rearrange everything back the way I like it best, since I do most of the cooking.
I try to keep them organized but we use so many so much of the time that they always get messed up again...so what I do now is just keep the ones that we use constantly up in the front racks and the less used in back of them and then the very seldom used in the very back racks.