If your shoes are wet, stuff ‘em with newspaper ASAP and keep them away from direct heat (which can dry the leather too fast, causing it to crack and loosen adhesives).
Throw out the shoe box. Storing leather shoes in its original packaging for long periods of time will do harm to the materials (thanks to humidity). Keep them on a shoe rack instead.
Put trees in your shoes. After conditioning and cleaning, cedar shoe trees are the best thing you can do for your footwear. They retain the shape of the shoe, reduce creases, and naturally absorb moisture/odors. Look for one with a full heel made out of unfinished cedar.
Give 'em the day off. Wearing your chestnut brown wingtips three weeks straight is definitely not going to prolong their life. Every few days give the shoes a chance to "breathe".
Use a shoe horn. That foot wiggle dance you do when trying to get your shoes on destroys the heels.
Add taps to the shoe. Much like the leather on the top, the material on the bottom of the shoe also needs to be protected. Shoe taps cost about $4 for a set, and act like buffers between your heel and the ground. They absorb the shock and damage of constant usage. However, don't add taps until you've worn the shoes for 12-18 months -- this gives their soles the proper amount of time to conform to your foot.
Three notes: Whenever working on your shoes with a cream, polish etc. you should a) lay down newspaper or old t-shirts on your work surface, b) do pre-test in an inconspicuous area on the shoe before applying it to the entire surface area, and c) put in a shoe tree.