Search for a compatible music partner. Make a list of possible cover songs that the two of you like and are willing to try to play. Search for songs with good, catchy melodies that are easy to follow.
Learn to play a few songs from the list. Pay attention to tempo and thoroughly learn all intros and outros on the guitar. Practice, practice, practice.
Use plenty of bar chords and steer clear of lengthy solos during your first few practice sessions. Get the tempo, chord changes and overall timing perfected.
Keep the practice sessions with your singer simple and comfortable. Try variations of picking and strumming to provide an option to the singer. Communicate your ideas and wishes openly with one another.
Have fun and experiment with the sounds you and your singer stumble upon. Try playing many different songs to keep the mood fresh, fun and exciting.