The easiest way is to hold the bottle in your dominant hand, look up and pull the lower lid down using the fingers or your non-dominant hand. This creates a pocket so when you gently squeeze the bottle a drop will fall in. As your eye only holds a half a drop, some will spill out. As long as you feel something in the eye, you did it!
Another alternative is to hold the bottle in your dominant hand, close the eye to be dropped, lift your chin, close your eyes and place the drop in the inner corner of your eye. When you open your eye the drop will go in.