How can I edit a long URL in the Safari browser on my iPad 2?
Hold down your finger in the address bar to get the little magnifier to show up, finally drag your finger to the right or left to get to the part of the url that you want to edit.
Update In recent versions of iOS, for devices with force touch, the address bar is selected, you can force touch the keyboard and slide your finger left and right to move the cursor.
ReUpdate Thanks for pointing out @Decade Moon, that in even more recent versions of iOS, you can hold the space key on the keyboard and move your finger left and right to move the cursor.