How can a zipper be pulled closed on a dress that has very small slider and the part you hold onto is shaped like a small droplet, there's so little to hold that I can't grip it properly?

Purchase an extendable magnet from a hardware or automotive store. These are designed to pick up screws that are dropped in hard to reach places, So long as the zipper parts are metallic, the magnet should work. You can also use a cord pull. Tie a paperclip to a string that will fit through the zipper loop Use a needle threader through the loop and pull the string through long enough for you to pull over the shoulder. Pull the open end of the string so that the paperclip can push the zipper up. Simply remove the string by pulling out the paperclip and string.