I start at about 5% below the "ideal" published load (not max load) and go up a little bit at the time.
Here's a good starting point if you're using the SMK bullets.
load map sierra 308.pdf
Also get a loading manual. Have at least one. I use the Hornady manual. On top of that, look for "good recipes" out there that match your rifle. All these are good starting points in developing and tinkering with a load.
Learn the different signs that indicate different scenarios. My 308 always seems to show overpressure signs (flat or slightly cratered primer) no matter how much I back off on the powder or adjust the C.O.A.L.
Most important in reloading is consistency. Do everything the same way. Ensure everything is the same, check, check, check... this gets you rounds that are predictable, and hopefully, accurate. :D