Hi achilles and welcome to the Cruiser's forum. You might flesh out some more details like where you are and where you are willing to go to hook up with a boat
If you are near water
already there may be opportunity at local sailing clubs. Particularly if they have race
skippers are often looking for crew.
for yacht clubs and sailng clubs in your area. Also if you can swing the money
it might help to take a dinghy
sailng course or a keelboat course to give you the basics.