Before i started flying i was advised to get my vision down to -3.0d, the limits for the class one. In the event I was given a class two which has recently been upgraded.
-5.0d is quite bad, I was -4.0 and managed to get it down to -3.5d.
Basically i followed a mixture of the bates method and other techniques. The most important thing to do is to stop wearing your glasses and contacts so much and buy all the books etc on the subject.
I was told I could get my vision to 20/20 I think this is a pipe dream. I think it is possible however to improve you vision by maybe 2.0 diopters if you work hard.
The other thing is, it's really boring.
Good Luck