My procedure that I got from my local marina is to do this all in order-
1) warm the engine
2) while warming the engine run your jetski on antifreeze.
(The second step would be hard but really all you need is a old plastic barel and a bildge pump. You can cut the barel so that it fits good around the pump housing,) now im not sure if your ski has it but usally on four strokes there is a port on the back where you screw in your hose to run it on water, if yours has this you can take a hose and fit it to your bildge pump- then all you need to do is hook the pump up to a battery, start the engine and connect the pump. Doing this and warming the engine together just ensures that all water is out of your engine.
3) (this step is if your doingna oil change as well) you want to rev your engine to 7,000 rpms amd hold it there for five seconds- when you hit five rip your safety lanyard off and now you can start to pump your oilvout (the only way to get the oil out is sucking it out of the dipstick hole.
You shoule be able to get 4 quarts out of your engine. After oil is out change your oil filter, should be black , metal cyclinder that has one bolt in the top of it-
then fill the ski with fresh oil.
4) pull your injectors off (two bolts one on each side of injectors) and lift them out, you wato to spray fogging oil into each injecto hole- after that put injectors back on.
5) HOLD THE THROTTLE COMPLETELY IN and crank it over for five seconds- ( the jetski will not start)
That should be it then good luck!