I prefer the use of lip slurs and trills combined with playing simple melodies as opposed to arpeggios.
The reason is that lip trills help to keep your lips flexible while arpeggios tend to make them stiff. Also by playing simple melodies one or two octaves up you work on musicianship and ear-training not just making awful squeels and squeeks.
Any melody will work Mary had a little lamb or any melody I have included Blue Bells of Scotland as an example. When you can play it up 1 octave then work on playing it up 2 octaves.
You will notice that it is more difficult to play a melody than to do arpeggios but it is much more beneficial as well.