Plant seeds in fine, level soil that's warm enough for the particular plants you're working with. Always check your seed packet before planting. Most are marked with the planting depth and space required between seeds and seedlings, as well as temperature suggestions. If you plant deeper than indicated on the packet, the seeds may not contain enough energy for the seedlings to reach the surface. Pay attention to how you space the seeds so you get the best results.
Some seeds are tiny and easy to sow too thickly.
Instead of sprinkling these directly out of the seed packet, take a pinch between your thumb and forefinger and drop them one by one into the planting site. You can also mix small seeds with sand to make them easier to spread. Experiment a few times, and you'll begin to get the hang of this. Or, if you don't mind paying a bit more, look for seed tapes, which eliminate the need for you to guess about application rate. Look on the seed packet for germination percentages.