Familiarize yourself with guitar chords. C. G, F and D7 chords are primary gospel chords. Gospel songs feature a lot of strumming on guitar rather than solo instrumentation; the role of the guitar for many gospel songs is simple accompaniment. Purchase a book of guitar chords and teach yourself a couple of new chords a week. You can purchase a chord book from a music store or find one online at no cost.
Practice your rhythm playing. This is the way you strum the chords. Since gospel guitar players primarily work as accompanists, the ability to play the rhythm in time and with a strong emotional approach is important. Gospel choirs are typically loud and energetic---your playing needs to match that. Practice daily playing the chords you learn with the emotion that should accompany a gospel tune.
Play as much gospel sheet music as you can. The best way to get better at playing gospel is by listening to it and playing the classic gospel songs. There are plenty of gospel music books available in music stores, and you can also find free gospel music for guitar online. Playing sheet music is not only a good way to build up your repertoire---it also teaches you gospel song structure.