I'll go with Soling42 here-- and the Loos people are the best. A few comments though--
Being a guitar player, I tune rigs harmonically. As long as there is sufficient tension, make corresponding sides sound the same. Is one side flat? --bring it up.
The Beaufort Scale says that rigging will whistle and hum at 22-27 knots of wind. If the rigging makes much vibrating or noise before that, it's too loose. A person should not be able to deflect much more than an inch or so by grabbing it for support.
The headstay should not sag. With a furler this tautness is hard to attain. Make sure the forestay is tight enough to facilitate headsail tension and match the rest to it.
Do not fight against anything-- nothing should seem impossible to move. If you can't get the mast to move back with the aft lowers, maybe the forward lowers are too tight. Look around. Make everything match.
Tune lowers before uppers. Tune the headstays before backstays.
Know the designed rake ratio and strive for it. (Headstays with furlers often foil you in this.)
Do the tuning in the water with the boat lightly loaded and level.
Make exposed threads of turnbuckles match. Don't have too much showing on one and not enough on another.
Eyeball it regularly, for column, lean, and rake. Don't ever go too far without looking up.
A compression post or deck structure in poor shape will make all these efforts only a disaster. Ditto for chainplates. Inspect all this stuff first. Living in denial (i.e., impatience to go sailing) will not ameliorate it.
I do work as a professional rigger and have never had an overly-loose or overly-tight rig to my credit and have never seen one go by the board... and this is how I do it. Take care and good luck.