If you see two front sights, put lampblack on the one you're not using.

More seriously:

I have two pairs of shooting glasses. One pair for handguns, the other for long guns. I shoot right handed.

For handguns I have +1.25 diopeter added to the distance part of the right lens. This makes the front sight tack sharp. Since they are bifocals I have +1.25 diopters taken off the reading portion to restore the reading portion to normal. Since the distance part of the left lens is still set for infinity I have a tack sharp view of the target through the left lens. Eye's don't see, the brain does. For most people this will look like both front sight and distance are sharp. There are a few people that it doesn't work for.

For long guns, I do as above except the add/subtract in the right eye is +1.00 diopters. Now comes the tricky part. You may or may not want to do this last part. I have the optical centers set a bit to the left and upwards so that when sighting a rifle, the optical center is closer to the line of sight with my head in aiming position. You can only go so far with this, not all the way. The drawback to this last bit is your view of the world is a bit cocked to one side when you are not shooting.

If you see two front sights, this indicates there is astigmatism at work. The glasses should provide a first order correction for astigmatism. This is as important a correction as the one for distance in many cases. Improper focusing for distance blurs the sight evenly. Astigmatism will blur it in an uneven manner and throw your aim off.

Another option is to go to the drugstore and buy the little past on readers intended for sunglasses. Get the power mentioned above. Take one and paste it on the aiming eye lens. Center it on the aiming line of sight. This will give you a correction for the front sight in a small area while leaving the rest of the lens and all of the other lens focused at infinity or target distance.

An old trick shot gunners use to correct cross dominance (Shooting right handed and being left eye dominant like me or vice versa.)is to put a small patch on the off eye lens to block off the barrel. As a temporary trial you can put a spot of vaseline in that location.