1. Start a Facebook group for shul members. Have a parsha discussion discussion start Sunday and run through Friday. The rabbi's sermon can address themes that came up during the week.
2. Let congregants speak instead of the rabbi's speech or in conjunction with it. Rotate guest speeches to include people who don't normally get to speak, particularly women. Bring in outside speakers who are interesting. The most engaging talks are the ones that come from nonprofessionals, speaking from the heart.
3. Hold interdenominational Sunday learning brunches together with other area synagogues. Encourage congregants to visit other shuls and bring back "best practices." Remember, it's not about getting the most money, i.e. members for your shul - it's about getting the most people to shul that we can.
4. Add more no-instrument music to service and/or shul events. Hold a chazzan competition. Make a "house band" and/or choir for Sunday dinner events. Have the kids sing...anything. Because it eliminates the usual judgmentalness and divisions between people, music is a great gateway to spirituality.
5. Guide people through the service in English. "In this part of the davening we..." Have page number clearly visible always, upfront. Have things to read for people who don't or can't follow along closely. Don't treat shul like an SAT exam.
6. Encourage people to dress comfortably (respectfully) not in a monkey suit. There is too much pressure to outdo the next person. Sell a shul-branded button-down or tee so nobody feels left out. Have extras in case somebody needs clothing. Not everyone can afford fancy clothes much less a shul membership. A bonus point is that the brand is a way to unite people in feeling like they are part of a community.
7. Have coffee, tea and pastries out in the hallway to make it relaxed and let people take a break. Have extra for people who are showing up hungry. For some people this is all they'll eat today.
8. Put an electronic slideshow on TV monitors outside the shul. Combine shul information, parsha information, and community news. Not everybody likes to sit in shul, but everybody likes to watch TV.
9. A couple of hours after shul, organize a Shabbos walk for Bikkur Cholim visits. Unfortunately, many people who observe Shabbos don't have much to do, leading to overeating, laying around, and even bickering. And not everyone can study Torah all day, or wants to. This kind of constructive activity not only helps the sick, but it also gives everyone something constructive to do and again, builds community.
10. Give people a chance to talk back to the shul leadership and the rabbi in a collegial setting. Instead of just laying out food for a kiddush once a week, take the opportunity occasionally to hold an open-forum discussion/Q&A session with the rabbi and members of the Shul Board.