“Just Friends” was composed by John Klenner with lyrics by Sam M. Lewis in 1931. It became a jazz favorite through Charlie Parker’s 1949 recording with strings and later versions by Chet Baker and Sonny Stitt. It’s one of the best tunes for learning how a song can start away from its home key and take the long way back.
The form is a 32-bar ABAC, commonly in G major (F is also popular). Instead of starting on the I chord, it opens on the IV chord, Cmaj7, then moves to Cm7 and F7 (the minor iv and the “backdoor” dominant). From there it slides into G major and works through ii-Vs into the relative minor, E minor, and other nearby keys. The C section repeats the IV chord idea before finally resolving with a turnaround.
For improvisation, the opening four bars are the key: Cmaj7 to Cm7/F7 to G. Practice the backdoor resolution by playing Eb (the third of Cm7) and resolving it to D (the fifth of G). After that, the ii-Vs are straightforward; use guide tones and resolve each one. Many players also hear the whole tune as a series of keys: C, then G, then E minor, then D, and so on. Labeling those on your lead sheet makes the solo much easier.
Practice by learning the melody from Charlie Parker’s string recording, then improvising one chorus using only chord tones in quarter notes. Play it in G and F, since bands use both keys. Slow it down to 120 BPM first, then bring it up to medium swing.
Memorizing the Just Friends Lead Sheet PDF: learn the form in sections, not all at once. Play the first eight bars until you can do them with your eyes closed, then add the next section. Within a week or two you won’t need the page at all, which is the real goal of any lead sheet.
Common mistake: treating the first chord as the home key. It’s not, so let your lines lean forward toward G. Read more about the tune’s history in Wikipedia’s Just Friends article, and find more standards on Minedit.