What occurs to me is that when a tune grabs me there’s a process that has to be gone through to learn it. The grabbing is an essential part of the process, and if I enjoy a tune, there's an almost irrepressible urge to sing it. Being compelled to sing the tune isn’t enough though, and it's good to know more before starting. Although I have good ears, it’s very useful to have sheet music for the song, preferably a few different versions. The ever-expanding music library on the bookshelf contains Real Books, Fake Books, downloaded sheet music and a variety of jazz composer anthologies. Given the nature of jazz, it’s common to hear a tune and later discover that it’s in one of those books already and you had no idea it was by one of your favourite composers. Greats like Harold Arlen wrote for stage and screen, churning out a big show tune a week so there are thousands of treasures out there to learn.
Once I’ve got my hands on the sheet music it's time to set about listening to as many versions as I can get my ears on. For standards that’s very easy, and sources such as spotify are invaluable for all of those versions you haven't yet bought. A lot of jazz standards started life in the musicals and if you're lucky it might have come from a film or a show that you can obtain a recording of. This gives valuable insight into the original meaning of the song. My Funny Valentine is a good example of this, and seeing the film (Babes in Arms) may make you change your mind about the meaning of the lyrics.
So now to set about learning the tune. If it's a well known melody it's easy to skip over this stage quickly, but in doing so idiosyncrasies may become habit, and errors become fixed. Singing the melody straight is very valuable as it can aid understanding of the song structure and how the sections are connected. So, it's a good idea to sit down with the sheet music, original and early recordings (Sinatra and Nat King Cole are good for singing songs "straight") and listen. Jay Clayton once told me that it's a good idea to listen to the tune ten times without singing before you begin. By which stage I'm itching to start, or to be more truthful, I just can't stop humming or singing for those ten times, but I pay close attention. Instrumental versions where the musicians play the head before and after soloing are useful at this stage too because different instruments may be playing in unison and have to play it straight.
The tune's in my head now, and I've absorbed the chord structure underneath from listening. I've still got the music in front of me and now to sing along, either to recordings, acapella or using music software such as band in a box. Unfortunately I don't have enough talent to play along with my songs (and the piano is on its last legs), but while I'm thinking about the melody I really have to consider the words of the tune. I'm not one for watching talent shows but when I do I get properly peeved with all the fake emoting that goes on in the singing. You can tell when it's real and when it's fake, really. If the lyrics are sad I want to be on the verge of tears when I sing it, at least while I'm learning it. There are many songs that I've loved and not been able to sing once I gave them a shot because the waterworks start, real ones, but in time they'll be keepers. Melody learnt, lyrics understood, then it's time for the fun.
By fun I mean playing about with the timing, the phrasing, the melody, and improvising. My natural style is to sing like I would talk which means that lots of fun can be had putting the natural rhythms of speech into the musical rhythm of a melody and fitting things around each other and making it my own. Listening to singers such as Ella Fitzgerald while learning a tune can be counterproductive, as you end up absorbing too much of her phrasing and improvisation and end up copying. It's good to be inspired, but when singing jazz in particular, you don't want to go mimicking the arrangements and quirks of other singers, especially well-known ones. You want to turn a hackneyed old show tune or standard into something shiny and new. If I'm feeling adventurous, there's the options of completely changing the melody for a chorus, scatting, or changing the feel of the tune, latin to swing to waltz.
And then the excitement of singing the tune with a live band. There's nothing like it, and it never works out quite like you expect, it's sometimes a disaster, but usually a revelation, no matter what.