To make a perfectly poached egg, you just need a few things. First, add 2-3 tablespoons of white vinegar to your water (I use a 4 quart pot filled ¾ of the way with water). Second, make sure you water is softly boiling. This is SO important, if your water is boiling too hard you will loose some of your egg white and potentially overcook your egg.
I like cracking my egg into a small shot glass before quickly dropping it right above the water. The shot glass seems to get the egg in a nice position. Also, you can scoop up your egg with a slotted spoon and blot the excess water with a paper towel. I usually take mine out as soon as the egg white is cooked and I lightly tap the center to make sure the egg yolk is bouncy and not firm indicating that it will be nice and runny.