When playing a slant, it's best to focus first on the intonation of the higher note. Once you are comfortable finding the higher note, turn your focus to the lower note and make adjustments with the amount of slant to be in tune.

Here's a good excercise for practicing slants: walking up from G to C.

E______________
C__7__9__11__12
A______________
G______________
E__7__8__10__12
C______________

The amount of slant (or angle of bar) will depend on where on the fret board you are -- slants that are higher on the fret board require less angle. So, always listen for the higher note to be in tune and adjust the note under it to be in tune with the higher note(s).