What marketing methods have you found to be the most successful at generating interest in your gym? We are especially interested in ideas for getting the word out about a new school that hasn't opened.
Facebook 
SEO had brought me the "highest quality" leads.
Facebook can get the word out. I also like rack cards in local business with lots of foot traffic. Local farmers market of you can get in.
Lol, recently I had a squad of 10 people go to door to door in gis and hand deliver flyers. But then again prior to BJJ I sold alarm systems door to door in Compton back in 2001.
SEO All day
Have ibjjf champs ;)
That helps not at all lol..
Haven't spent a penny on seo. I did create as many social media accounts as I could for the gym... Facebook, 4square, yelp and so on. This is the poor mans way of getting your school to the top. Nobody at my gym uses anything but Facebook, that said all the other link will pop up when searching for the school.
So far my biggest contributor to gaining new members is word of mouth.
If you wanna get students fast. I recommend doing a community event.
Bully Bootcamp for Kids
Women's Self Defense for the ladies.
Both of these will help you business tremendously!
For starting up, we have found banners (professionally made) hung around town (at traffic lights where cars stop for a bit) worked brilliantly. Signage is our best value paid advertising method - expense vs results.
Facebook ads to drive people to your Facebook page and website will work ok but is getting expensive so be sure to target your audience and have a special offer to entice them in. Works well for our kids classes.
When you have members, a referral program is your best bet. We have VIP cards that members can take, put their name on and if someone brings that card in (the card gives 2 week trial membership for free) they go into the monthly draw for a free months training - if that person joins as a member the get 1 month free as well.
We sell it as they get 12 people to join our club, they train for a year totally free (or more with 12 chances to win in the monthly draws).
The best advertising is the recommendation of someone who already loves training with you.
Nice referral tip Rob ;)
The 2 Best ROI have to be a great website (including SEO) and referrals.
Unless you have plenty of money, don't bother paying someone else to do these. Learn to do them yourself, and learn to do them well. Almost every student I ever had came from those two places.
Thumbnail sketch:
1) Your website isn't about you. Stop talking about yourself and what you offer. Your website is about the person reading your website. Tell them how you will help them.
2) Invest your time and energy in your students. Care about every person who steps into your gym. You need to want for them all the things they want for themselves.
These are the two greatest sources of more students.
Personally it's always been flyer drops and running programs for school kids
Lots of 5 star yelp reviews. I've done some advertising with yelp and it's been meh, but I have a lot of reviews and have a link posted to my homepage.