I exfoliate my arm really well and then make sure it’s nice and dry before putting the sensor on. I’ve not had one fall off yet, they’re still well stuck on at the end of two weeks.
I’ve used the Libre for a while now and I always exfoliate my arm with a body scrub and then rub with surgical spirit and let dry before applying the sensor. Touch wood, mine have always stayed on even when swimming a lot on holiday. They’re still hard to remove after the 2 weeks is up.