all depends on use. typically mine will be daily driving, spirited or towing.
unless i am towing or have a vehicle w/ E rated tires, i never go above 37 warm.
with towing , i use the card trick
for daily driving, i am usually @ 33-34 cold. that puts me @ 35-37 w/ tires warmed up.
if i am doing spirited driving on a track, i'll start @ 30-32 as my tires will get really hot in corners. this will get me to 35-ish hot. then i';ll have to check temp/wear & make adjustments as day goes.
i typically use playing card, temp or chalk trick to figure out what works best to start.
(as of late, i like temp & card tricks, best)
1) temp -
take temp on tires cold...inside/outside edge & middle for all 4 tires. then go for a 10-15 mile drive on highway. back home on a flat surface, check temps again. if the center of the tread is cooler than the outer sides...the tire is under inflated. if the center is warmer than the sides...then you are overinflated. if the outer tread is warmer than the inner or vice versa you have a possible alignment or carter/camber issue.
2) playing card -
on warm tires, inflate w/ air until you can slip a playing card under tire to edge of 1st lug. then slowly deflate tire until card drags on removal (if you cant remove card, you deflated too much)
3) chalk method is tedious for sure.
[concrete is actually the best choice, but you can also do this on asphalt.]
on warm tires, color a section of your tire with chalk to see how much tread is making contact with the ground. on a flat road surface. make a mark with soft chalk that goes all the way across your tread. then, gradually drive your vehicle forward about 50-60 feet and then backwards to starting point. (50-60 feet)
check out the chalk on the tire. if the chalk is only worn off on the center of the tire, reduce the tire pressure slightly and go through the process again. with the adjustment, you should see the chalk wear off more completely. keep making tiny adjustments in the tire pressure until the chalk wears off evenly and all the way across the tread. reapply chalk as needed for testing. you must complete this process for each of your tires.