This is what I have done in the past when my ski sank:
I first checked the charge on my battery, and made sure the battery was charged.
If the motor turns over, but won't fire, you're in an OK position.
If the motor won't turn over, remove both plugs and give it a go.
If it won't turn over at that point, you're in for a challenge. At that point I would try to spin the coupler by hand inside the hull (with the plugs removed).
With both plugs removed, turn it over for 3-5 seconds. If water is coming out, you've gotta get it all out.
Put one plug back in, and with your finger cover 90% of the hole and turn it over for 3-5 seconds.
Switch the other cylinder, and do the same thing. Keep doing this until most of the water is out.
The next trick I learned from Mark44. With a friend, spray WD40 down one carb for 2-3 seconds, and switch to the other carb while the friend tries starting the ski with the throttle pinned wide open. Do this for about 10-15 seconds. Make sure there is spark on the spark plugs before doing this.
Good luck.