Brainstorm ideas for the song. What is it that the song needs to say? Write down keywords that express the feeling of the song. Think of moments that exemplify the friendship. Think of the emotions the friends generate. Write down what each friend brings to the friendship.
Select a genre for the song. Selecting a genre like folk, rock or country will help you envision a beat and melody. The song can be humorous, and does not need to be serious.
Write the lyrics. Listen to your favorite songs and read the lyrics for inspiration. Lyrics are similar to poetry, and the words should flow into one another. There is no formula for creating "good" lyrics. The process is creative and tailored to the song. The lyrics should include a few verses, a chorus and additional verses. Two to ten lines of verse, and then a chorus is a basic structure for many songs. Add an additional two to ten lines of verses, another chorus and additional verses for a longer song.
Sing the lyrics. When the lyrics are sung it will be quite obvious what works and what does not. The lyrics should flow into one another melodically. If they do not, then they need to be tweaked. You should imagine what sort of accompanying music will go along with the song when you are singing.
Hire or find musicians to play the music. Sing the song for the musicians and explain to them what you envision for each instrument. Experienced musicians should be able to pick up on your ideas quickly. Sing and play with the musicians until the song sounds like you want it to.
Share the song with your friends.