I have never run a subreddit, but it seems to be an ordinary scheme:
1. Create a sub;
2. Find here (on BHW) services providing Reddit upvotes;
3. Make posts on similar/thematical subreddits (if your sub is about outdoor, you can create posts on the /earthporn, /hiking subs, for instance);
4. Upvote your posts and launch it to the top;
5. Get new subscribers;
But it all depends on a) your subreddit theme, b) whether your subreddit interesting or not (why should I subscribe on you, so to say), and c) upvoted post quality. If you'll create a shitty post, it doesn't mean how many upvotes you'll buy.