You know that little blue strip on your razor that tells you when to change the blade? It lies. One of the main causes of dull blades is that the cream and water left on the blade will corrode the metal, making the blade more dull. My trick? Rinse the blade in a little alcohol and gently dry it with a soft cloth (or better yet, run a blow-dryer over it). Just make sure to be careful not to cut yourself or damage the blade. You can then continue to use the blade as long as you're getting a comfortable shave without irritation. I'm on about month six with my current blade and it's still shaving just fine.
When shaving, just be sure to do it right.