There's more than 1 way to help a site succeed, but simply put we have to be very careful of how we manage it.
1. Be Patient
I'm sure you're thinking of many questions, but don't post all of them on day 1, that leaves no other questions for other people to ask, then the rate of questions asked will drop and the site will become inactive. Try and space out your question asking, and if you see the site has a lot of questions one day, maybe wait a day before asking yours.
2. Maintain a High Standard
There's no point making rushed questions or answers, trying to post as many as possible to fill the site not only effects the above point, but also makes for poor core questions. The questions made at the very start are more likely to be ones kept for the life of the site, often ones that introduce people here, so they need to be of the highest quality. Take your time making both questions and answers, and if you don't feel confident in making a good post, don't make one, let someone else make an amazing post.
3. Make users here the best you can
It's all well and good to say "Get as many people as possible" but then you have the above issue. If they don't know how to post questions or answers, they will fill the site with horrible questions and answers and clog up the system. If you see a new user (or any user) that's asking poor questions, instead of deleting and downvoting the post, try and help them improve. Having more good users is never a bad thing, and if you can help improve the quality of a user's work, then that's a win for the site. It's better to improve 1 user than to turn them away.
4. Be Friendly
No matter what's happened, how much you disagree or how bad a post is, always keep cool. Manners are an invaluable tool, and will get you very far. You don't want to be "that guy" that everyone dislikes because of his way here, and in addition you don't want to be remembered by new users as that 1 guy that told him his post was useless. Always use constructive criticism, even if they post bad content, maybe one day they can become an amazing poster, and you can take pride knowing you helped them achieve that.