What do you look for/do while you are practicing long notes? I think that is going to be part of your answer as regards to the process and development on tone.mendipman wrote: Once the basics are gained what exactly is the process of development and signs to look out or aim for?
One instructor likes saying "[Developing on the flute] is a question of time, patience and intelligent work"* and further remarks
(Source: Trevor Wye's Practice Books for the Flute: Book 1 Tone; italics in the original)...if a student plays long, slow notes to give him opportunity to examine his tone in close detail, then provided he can hear the undesirable aspects of his tone, his self-correcting mechanism will ensure that it improves. Long notes really can't fail to improve your tone! Nevertheless, long slow notes played without care and thought will not achieve any real result quickly.
So that is why I ask "What do you look for/do?" A teacher can best guide, help and point out areas for work, but if you can listen discerningly, you can improve and progress on your own.
*The statement is Trevor Wye quoting Marcel Moyse' De la Sonorite; that is, one flute instructor quoting another.