It depends on whether your using zoom lenses or fixed lenses.

On zooms you'll have the inifinity symbol with a horizontal L - you line up the upward leg of the horizontal L with the zoom factor which will normally be written in RED. This will however not give you the minimum focusing distance but if you have a DSLR then press the Depth of Field Preview button to check what's in focus and then correct.

I never worry about it I just use the above method and never have any problems.

Roger