I always start by letting the software handle as much as it can.
Leave the degrees of rotation set to off, put FFB and shck to 100, ABS to wherever you like it, then I leave drift mode off, linearity at 0, centre spring at 0 and dampening at 0.
If that doesn't feel right the first thing I'll usually do it mess with the rotation, som games need to force the 900 to match the wheel on screen to your wheel in your hand. Other games like F1 games probably need around 300 degrees so that you never have to go hand over hand.
If it still feels bad I put the spring up to give it some tightness, and if it STILL doesn't feel good I will start messing with the linearity and stuff. BUt honestly the only game I can't get a great feeling with is DIRT 2... I seem to be really slow in it compared to using a controller.