heres a straight up procedure I was taught a few years ago; have a full supply of air in the system, block all the other wheels, release the park brake and confirming no vehicle movement then jack the wheel off the ground you are adjusting.
dot best spec is 1/2"-3/4" rod movement, this also should be correct rod angle if any major replacement was done as the angle should have been set proper by the wrench doing it.
or that's what I was tested on.
When adjusted to a full loc or applied, I was taught its best to first check that no drag at 1/4 if so 1/2 that's the reason for jacking and I'm sure a lesson for myself, it was a good one. If there was a drag a wise choice to take a better look and usually remove the cover for a look see.
If you happen to be close to a truck shop at the parts counter they probably have a stack of card board or even plastic angle measure "templates" given to them by the brake mfg's. they pass them on to the techs and customers.
any more questions feel free to ask
have a good day