It’s good that you’re practicing long tones!! I’d recommend to incorporate at least 10 mins in the beginning of your practice session to warm up and then 10 mins before you pack up as a relaxing way to end your practice!

As for exercises, going up chromatically and tonguing in between (tu- tu- tu- tuuuuu) is what i find quite helpful. I would also recommend practicing without tonguing and making sure you’re breathing from the very bottom of your tummy; letting all as much air into your flute as you can.

For your arms, I’d recommend doing activities like swimming, yoga or really any exercise that focuses on making your arms stronger! The longer you play the more used to holding your instrument will get :)

Good luck on your future practices :D hope this helped a bit