After I have learned a new song it takes still several months before I'm able to improvise on it without losing the chord scheme and without having ridiculous melodies. During these months I need points of support. I play the characteristic pieces of the tune in the original way and limit the improvisation to the other, more common, parts. The more I know the song the less support I need.
It is not difficult to find these points as you automatically will meet them as soon as you start to improvise on the song. In the beginning nearly the whole song belongs to the area where you are not able to improvise, but by playing the song over and over again this area will gradually get smaller. A thumb rule to find points of orientation is to look at the first words of each sentence.
As an example I will play the song 'If you were the only girl (boy) in the
Hear the song.
I have learned it only recently and I still need points of support. I have underlined them. These pieces I have learned so well by heart I will always be able to find them, even if I have lost my orientation.
If [G] you were the [E7] only [A7] girl in the world
And [D7] I were the only [G] boy
Nothing else would [Gdim7] matter in the [Am] world today
[D7] We could go on [Daug] loving in the [G] same old way
A Garden of [E7] Eden [A7] just made for two
With [D7] nothing to mar our [G] joy
I would [Gdim7] say such [Bm] wonderful things to you
[Am] There would [D7] be such [G7] wonderful things to [E7] do
If [F] you were the [Gdim7] only [G] girl in the [E7] world
And [A7] I were the [D7] only [G] boy.
The pieces not underlined are meant for improvisation, but the chord
scheme and the measures must stay in their original position. The
melody may be completely different, but has to agree with the current
temporary key, which will give no difficulty if you are musical. At the
most you will make mistakes, but these will decrease the more you
improvise on the song.
Hear what I mean.
As you don't play the song always in its original way you will be able to
carry on playing it many times. Every time you invent new melodies for
it (and it are the most beautiful ones because they are your personal
choice for the moment).
Hear what I mean.
I know the song 'It's a long way to Tipperary' so long I don't need points
of orientation any more. I will play it and then improvise on it without any
point of orientation.
Click to hear it.