It is a good idea to do your sowing in stages so that in the event of disaster you have a second chance. Depending on the size of the seed you may have to create a seed 'trench' or punch a row of small holes with a dibble stick. The rows should be at least an inch apart. The planting depth is critical but is usually one or two times the diameter of the seed. Very fine seeds should not be covered at all, nor seeds that require light for germination.
Some seeds come in a petteted form because of their size.
These should not be covered at all, but merely pressed into the surface of the mix. Carefully distribute your seeds onto the medium or into the small holes, using care to be sure that they are not crowded. This will ensure room for growth as well as good light and air circulation to the seedlings as they develop. It will also make it easier to transplant the new plants when the time has come. Now you should create a miniature greenhouse environment for the pots or flats.