Marketing is key in any good business, and just like other businesses you need to maintain a presence in your customers mind. There are many simple and inexpensive ways to keep current in the public eye. In my opinion fliers are a crucial element. Anytime you perform you should have a way to drive fans to the next step. Whether it is to buy a CD, check out the next show, visit the website, or anything else fliers are typically the easiest and have the quickest turn around.
Social media tends to be the most obvious for people today, but there are methods and patterns to using social media as a marketing tool. Social media is not solely a 'push' style method, fan interaction is key to keeping an audience. If you don't engage your fans or indulge them with viable content then your social media efforts may not pan out so well. This is an area where the more genuine you are the more fans will respond. Besides would you rather have 1000 likes from people that don't care or 400 likes from people that will share your message and listen to your music?