Conservatively is probably the best advice. Turning it in moves the engagement point out, lifting the clutch pressure plate higher. I've had success screwing it in one turn or less (after picking out that crusty gunk Ducati seals it with) without a problem, and that adds quite a bit of lift to the clutch. If you go too far, the master piston can block the fluid return port when you release the clutch. Without a return path, fluid pressure in the line will build up, especially when the fluid and air in the circuit get hot. This can cause the clutch to slip and increase wear on the pushrod, throwout bearing and slave cylinder. Mild slipping that you don't necessarily notice will wear out your clutch quickly.
One way to tell its working right is to remove the reservoir cap and look carefully for return flow (a little squirt near the piston) when you slowly release the lever. Wear glasses, in case you let it go too fast!
Note that the adjuster's position is secured by not only the gunky glue covering the screwdriver slot, but also by a tiny allen set screw in the bottom of the pivot barrel. You need to loosen this set screw a few turns before you try to adjust the plunger adjuster.
Hope that helps!