I'm about to start a lot of herbs and flowers with tiny seeds - seeds that are much too small to handle either by hand or with tweezers. I still want to plant only a controlled number per cell, though, so I want to plant them individually. The trick is to use a dampened toothpick. Dip the end of the toothpick in water, touch it to a seed, and then touch it to the potting soil. Most of the time it will transfer to the potting soil, but occasionally you'll have to wipe it off the toothpick. Clearly, these are much too small to start in paper towels, too. They need to be planted directly in germinating mix or potting soil. They don't need to be covered with more soil! Very few seeds do. But you will need to see that the surface of the soil doesn't dry out, either by covering with plastic until some seeds start to germinate, or by misting lightly periodically.
The picture shows one arm of a tweezer with the tip of a toothpick resting on it, with one snapdragon seed on the end of the toothpick. I've shown one cabbage seed with the snapdragon seeds for comparison
Update: This is what some of the tiniest seeds look like 3 weeks after planting: