I'm assuming you have a boost gauge, right?
Once you have it installed, adjust it to low boost. Really low. Basically as low as you can adjust it. Then go for a drive and see where your boost is. Then adjust it ¼ turn in, and try it again. You'll have to do this many times, but it's better to go slowly than to adjust it too much and hurt something in the engine. Once you get it close, you can fine tune it by just barely turning it in until it gets where you want it.
Also, I forgot to mention, test it in 3rd gear, or going uphill. You need to put a load on the engine for it to work properly.