Web and social media presence is of utmost importance in getting your band booked. If the client can't find you online or your sites aren't professional, you won't get booked. We can't begin to tell you how many bands have approached us for bookings while having no website, a sub-standard site, or little to no social media presence. In our socially media driven world, there really is no choice but to make this a top priority.
Starting with a nice website is best. There are lots of ways to build a site and several of them are free or inexpensive. Businesses looking for corporate entertainment don't necessarily want to go through FB pages to find information. Your website should have quality pictures, audio, video, a sample song list, contact information and a calendar with dates. Don't overthink it and don't put too much added material on it as the average attention span isn't very long. What you do choose to post should be high quality and the very best representation of your band. Spend money on good photos and a professional video if possible.
Reverbnation is a great second step. It's free, easy to navigate and functional to use and manage. Some bands still use myspace as well. A band FB page is a must, especially if you are trying to get good club gigs. The potential clients will look at your page for activity and also the number of followers and likes you have. Make sure you put the effort in weekly to build that base. It will take time, but it will be worth it in the long run.
Always link all of your pages together. Everything should have a cohesive look and be easy to access from all of your sites. It should go without saying but...you have to be good to be sold so be GREAT!! Much more on social networks, marketing & branding later.