Well do you want real people subbing? Because i think you can buy subscribers somewhere on these forums. But if you want real people subbing you can maybe edit your video saying "please subscribe for more videos" something like that
Contest will work but its kinda like sub 4 sub becuase after the contest is over those people probably aren't going to watch your stuff. There used to be something on you tube called the get viewed network where people did what you proposed in one of your post about watching each others videos and rating and commenting. Don't know if it is still around because that was a few months past and that can be forever in YT land.
