What is the structure of a good arrangement as they used to do it in the good old twenties and thirties? 

First an introduction is made, after which the theme is introduced by the trumpets and the trombone who play three-part and synchronously – answered by the saxophones.The theme is repeated, but this time by the saxophones and answered by the trumpets and trombone.After that a transition is made and now the key changes  to match the singer’s voice. Now the introduction and theme are played for three voices. After another transition there is a change back to the first key.There will now be room for soloist improvisations before the key is changed again and the final chorus is played. In order to make arrangements like this, all musicians must be able to read notes.