Buy a service manual for your vehicle? I have yet to see an important fastener without a specification (torque and pattern).

If you are a professional mechanic, it's your responsibility to obtain the specifications and follow them. This is especially true when it comes to a licensed and certified A&P mechanic and not your neighborhood shadetree mechanic.

If you don't know what you are doing then better stay away from anything critical. There are 'stretch' bolts, bolts that are definitely not to be overstressed or they'll weaken and bolts that will cause damage to whatever they're bolted into if over torqued. Every workshop manual and every workshop process has specs for all fasteners.

It gets worse when bolts and part are of different materials (say: steel bolt in aluminum part), that's a very nice recipe for trouble (also in the long run, not just during assembly because oxidization will almost certainly occur on the interface and oxidized metal takes up more room than clean metal so unless you very explicitly protect against it the fasteners won't come out without massive damage to the part).

Workshop manuals are your friend.