use a zip tie on a fork leg. that will measure the sag. what is it that you are trying to accomplish? handling or ground clearance? changing rake will alter handling. raising ride height will increase ground clearance. the lower the front end, the quicker the steering. raising the rear also accomplishes this.
adjusting compression and rebound is for high speed cornering. it's best to set them at the middle for street.
tire pressure is also part of the bike's suspension. fork spring and oil tuning gets too involved for DIY. after market rear suspension is the way to go.