depends if they are tapered or straight. Tapered gibbs will have usually have a screw lying in the same axis as the gibb that advances it in or out. as it is tapered, advancing it in or out tightens or loosesns the gibb. lesser machines have screws/set scews along the dovetail at 90 degrees to the gibb. if thatís not clear I could snap some photo's. I don't know how to tell you how tight to make the gibb, except that running them tight increases wear but makes things more rigid. I just snug up the gibb screw and back off Ĺ a turn or so until it feels right - if you have a heavy duty job, tighten them down more.
use oil. Way oil (sticky) is what I use but some dislike this claiming the chips stick to it. if you use regular oil, 30 wt non detergent is good. If the machine doesn't have it, install some sort of oiler so you can get oil to the contact surfaces of the dovetail.