Using weaker prescriptions is fine, but here's one tip to increase the likelihood of success:
You have to be cautious that you don't make an effort to see clearly through the weaker prescription; this is particularly likely in the initial stages of wearing weaker glasses when your eyes are used to seeing more clarity. A good practice is to intersperse the weaker prescription with wearing no glasses at all - quite soon the wearing of the glasses will seem incredibly clear, and it's possible to move forward into a more relaxed and natural way of seeing.
A good rule of thumb is to go for lenses that give you about 20/40 (6/12) accuracy. That's usually close enough for the eyes to figure out how to let go a little bit, and ease into the lower refractive error.
(Good luck!)
BD