"Left side click to reduce value - right side click to increase" is the best option for me. It works everytime, everywhere.
...and it sucks big time on ALT, HDG or SPD knobs. I am much quicker with the mouse wheel than pinning down or, worse, endlessly mashing the left or right button.
On knobs with less than, say ten possible positions (ex. autobrake) it's a viable option though.
Click and drag should only be used for elements of secondary or tertiary importance, like cockpit windows or similar, as it's highly view-angle dependant.
And as for camera manipulation, the "ALT+[Mouse]" combo suggested in the first commentary is just fine.