I have spent many years supplementing my income as a freelance musician. The work is generally enjoyable, pays well, and often takes little time out of my schedule. Here are some of the things that I have found tend to lead to getting gigs.
Introduce yourself to as many people as possible in the music world and let them know you are interested in working. Local music teachers and faculty members at universities are often the first people who know about potential jobs. Owners or managers of local instrument repair or supply shops are also very knowledgeable when it comes to performing groups.
Familiarize yourself with local churches. Many churches, particularly those with large congregations, hire musicians for special programs. Christmas and Easter are generally the busiest times. Some may also have special events centered around spring, Valentine’s Day, Back to School, prom alternatives, revivals, etc. Introduce yourself to the music minister. You may even begin with volunteering some of your time. Volunteering can often lead to paid work in the future.
Join a community band or orchestra. These groups are often loaded with great people connections. The group to which I belong consists of members ranging from middle school students to teachers to semi-professional musicians. Some of the more serious musicians belong to other ensembles in addition to our community group. Knowing and playing alongside these people has often led me to paying gigs with churches or small ensemble groups. You may even find that you can start your own small ensemble (quartet, jazz combo, chamber group), with other members. Even if your newly formed group doesn’t get any paying engagements right off the bat, the rehearsal time together helps to hone your skills and can be great fun! Again, volunteering your time and talents with smaller groups can often lead to paying gigs.
Become proficient on more than one instrument, or on a less common instrument. Trumpet players, saxophonists, and percussionists are usually very easy to find (and very eager to work). If you play one of these, consider developing your skills on French horn, keyboards, or string bass. Also consider learning a new instrument if your proficiency is on one for which there is less need, such as clarinet or oboe. Many times, people are looking to hire brass quintets, quartets, or jazz combos, so if your instrument works well with one or more of these you should be in good shape.
Expose yourself to and become proficient at playing a wide variety of musical styles. Jazz, big band, and classical are usually the most sought after, but it is helpful to be familiar with as many different styles of music as possible. Familiarize yourself with various forms of pop, gospel, bluegrass, or any other style, particularly those most popular in your area.
Most important is getting your name and talents known by as many people as possible who are connected to the music business. Meet people, play with groups, and volunteer your time to expand your connections and keeps your skills sharp. Hopefully the above suggestions will help you on your way to achieving your goal.