Mix thoroughly with a trowel or your bare hands, between waterings. Keep adding water until it feels like a wrung-out sponge. Most seeds should be planted twice as deep as the seed is thick. Some seeds require light to germinate and shouldn't be covered at all. So, always read the seed packet.
Seeds germinate better with bottom heat.
If you don't have heat tapes, sit them on a radiator, the fridge, or other warm place. As soon as the seeds start to germinate, remove them from the heat. Set them on a sunny windowsill or under grow lights. Otherwise, they will get tall and spindly. Water seeded flats and seedlings from the bottom, or from the top with a spray bottle.