As a veteran motorcycle submariner, I advise don't do it. But if you just have to............. don't try to start it right away. Wrestle it out of the drink ASAP. You will need to drain the exhaust out so lay the bike over pointed uphill and exhaust pointed downhill. As mentioned, remove the spark plug and crank it over with the throttle open. Crank it A LOT. If you try cranking it without removing the plug and there is water in it, you can hydraulic the engine and bend some expensive and important parts. If you picked it up right away, you probably won't have water in the fuel so that isn't a big worry. You will want to remove the air filter and wring it out. When you put the plug back in and try starting it, it may water foul so you may need to remove and dry the plug several times. After it starts, ride it as gently as possible to get it home or to the dealer and ASAP do a major service on it including oil change, air filter service, chassis lube, cable lube, chain lube and general check over for any stray trouts or crustaceons.