For a homeowner who does not have expensive saws, the easiest way to cut down the type of blind you mentioned is to use a pair of tin snips on the metal head rail and metal bottom rail. The cut on the head rail will be hidden by the brackets so a perfect cut there is not important, but the bottom rail cut will be seen, so take extra care when cutting it for cosmetic reasons. For the vinyl slats of a mini blind, use a pair of scissors. To achieve a professional look you will need to go back after the initial cut and carefully round the edges of the slat, While a previous respondent mentioned that it was advisable to cut both sides down evenly, one can only cut down one side if it is 1/2" or so and not have the symmetry visually noticed unless one tends to be obsessive compulsive. I would also warn that before cutting down the head rail to mark where one intends to make the cut, then hold the bracket up to the head rail where cut will be and make sure that when cut the bracket is not going to be jammed up into the tilt or locking mechanism. I would also recommend that when cutting just one side that it is the right side of the blind. Most people are right handed and thus it makes it easier to do, but more importantly so as to not interfere with the factory spacing on the left side because when raising or lowering the blind with the lift cord, it will tend to gravitate to the left and jam up into the window casing, causing problems. If the jamming up to the left side is a problem when cutting down or installing blinds that fit appropriately, most blinds have a piece on the end of the head rail that has small tabs that can be bent out to create appropriate spacing.