If you are using standard eye droppers, use only plastic ones. The glass kind have far too much variation in them to be repeatable for photographic use. Plastic droppers are medical grade and the openings are cut and sized at the factory for consistent drop size.

For the most consistency, I always lift the dropper straight out of the amber bottle, then over my shot glass. I never turn the dropper horizontally as I count drops, as I've often seem, because I find that the drops will cling to the side of the dropper, sometimes giving very small drops, and other times very large.

As others have mentioned, glass pipettes are extremely accurate and are kinda cool, as well.