I've always used 30-35mm for a street bike, and 25-30mm for a track/race bike. Around a third of the overall suspension travel. I usually set my front and back the same(within 2-3mm).
I have always used the racetech method for measuring sag:
http://www.racetech.com/page/title/Sag
Andrew Trevitt's book is a great read and I would highly recommend it for something looking to start adjusting their own suspension.
https://www.amazon.ca/Sportbike-Suspension-Tuning-Motorcycles-Performance/dp/1893618455
I got mine from Accelerated Technologies if you want to buy local.
The racetech suspension bible is pretty dry but also a bit more technical once you get your head around the major concepts.
https://www.amazon.ca/Race-Techs-Motorcycle-Suspension-Bible/dp/0760331405
Dave Moss' videos are very informative although I do find he can contradict himself at times.
http://feelthetrack.com/free-vidoes/ustream/