For short term gains?

Just lie to their face and sell them unrealistic dreams about going abroad, like all the other crap schools do.

For real long term success?

Make the effort to actually learn some basic shit about marketing, be sure to understand the needs of your target consumers (or create a need) and somehow offer a decent service to offer to customers; actually hiring real decent teachers and then retaining them does go a very long way.

The fact that you've had to even ask this question suggests that this is something that you aren't familiar with.