Nat Kline wrote some very helpful exercises to practice fourths after he saw Dan Gaynor's Fourths Exercise. Nat designed a template that covers the entire range of the saxophone (or flute depending on where you start). He calls it a 'template' because he meant for the player to play through it while adding different key signatures each time. If you're ever tried to practice fourths you'll know that it is sometimes confusing when you come to the bottom or top of your range, because it can be hard to determine how to turn around smoothly. By adding your own key signatures you are also forced to think rather than just reading through the exercise on autopilot. Often improvisers get stuck in the rut of playing either horizontally or in thirds, ignoring wider intervals like fourths, fifths and sixths.
Fourths Practice Template