Many people mentioned getting a sharpening system and using your knife to get a feel for what kind of improvements you would like. Thats very good advice. (You can stop reading now ;-)
Next, buy/use (or at least handle) knives that are radically different from what you just bought. Benchmades, Kershaws and Spydercos come to mind, but also others. Go to a real life store to handle them, say you will think about it, and look up prices online to see if they can be had for a lot less. Then decide if its worth something to you to pay more, in order to support local merchants. In these economic times, that point can't be stressed enough. Ask for a discount if the price is ridiculous compared to msrp or online prices.
That will give you an idea of what you like and don't like about different locks, materials, shapes, steels, etc.
Also notice differences in manufacture quality and prices. Look for symmetry/evenness in the metal, scales, etc. Ignoring those things were some of the reasons I started out buying really crappy blades back in the day, along with ignorance of what makes a good knife.
-MD