Seed wants to germinate, by its very nature there is nothing more important for a seed to do, and with your help, it can. Seeds, however, have built-in mechanisms to prevent them germinating at the wrong time, or in the wrong place, so it is up to you to convince the seed that everything ready to go and safe for it to germinate. For some seeds, like most annuals, this is as easy, but for others it may take some effort to trigger all the necessary mechanisms to begin successful germination.
Seed should be planted at a depth equal to the length of the seed. In the case of small seeds, a fine dusting of sand is best. Some seeds require light for germination and must not be covered -please refer to the specific notes for the seed variety, or consult with a good book on seed starting and germination.