Well, gas or elect.? if elect. just make sure the water is drained and store it in a dry place inside would be nice where temp. changes don't create moisture.

gas IMO you want to drain the gas tank most likely it got some water in it from acidently spray, I also swab out any residue. I make sure the pump is drained by tipping it all directions. I also spary some WD40 down the connections hoses and on the rubber o-rings and seals. I also make sure the hoses and nozzle gun is drained of water and spray some wd 40 inside to help condition the seals. But, thats me and I always go overboard!?! others may disagree.

The only thing I do with mine is make sure that the gas tank is empty and I store it in my basement because I don't want the pump to freeze.

After every use I make sure to get as much water out of the pump as possible. I also completely drain the hose and wand.

I've only had mine about 4 years so I have no idea if what I am doing is a good long term plan :p

just make sure that all the water is out or look forward to replacing a cracked housing at the very least in the spring.