When ever possible we skip tray seeding and just seed directly into our garden like nature intended. Direct seeding varies greatly depending on variety. One way is how we seed our sunflowers, or any seed large enough that can be easily handled. We enrich our bed with compost or fertilizer preferably a week before seeding. We then till to a depth of 6" and to a bed height of at least 6", until the soil is a fine consistency - like that of brown sugar. We use a gas powered walk behind tiller but you can use an electric model, or attachments that go on lawn care equipment such as trimmers. Another way to take a pitch fork and turn the soil over until you get the right soil texture. Bottom line is no seed likes to go in hard compacted ground.
Once our bed is ready we like to use a stick we pre-mark with a few depth marks, or you can just use your finger. Sunflowers like a depth of 1/2" to 1". Planting seeds deeper than the recommended depth means your seedling will struggle to reach the surface which can decrease your germination rate. On these sunflowers we are going down 1/2" and then insert our seeds. We use the back side of our rake to smooth out the soil. We then like to add a light dusting of compost. After seeding be sure and water so the soil makes good contact with the seed. We generally don't presoak our seeds unless it is later in the summer and the conditions are very hot and dry.
If you are dealing with smaller seeds such as celosia, or poppies, we use a shaker method. Some people will use an unused salt shaker but we have found the holes are too small to accommodate different seeds. We use this parmesan cheese shaker we bought at the dollar store, or you can use a cleaned out spice container, as long as the holes are big enough for the seeds to easily pass through. We then add fine play sand, or fine vermiculite, to our shaker. Make sure your sand is completely dry. The seeds are then added and the contents are mixed with a spoon to ensure even distribution. We then shake the contents the area we want our flowers to grow. Depending on variety we then top with some fine top soil, compost, or for seeds that require light sand. Down side is once your seeds germinate you will eventually have thin them out to proper spacing, but we guarantee these seedlings will grow better and produce more flowers than tray grown seedlings.
In this next picture we have a Scabiosa seedling that we started in a tray inside in mid January and put out into our garden in mid April. This picture was taken mid May. It's hard to tell but this plant is about 6" tall.
This plant will eventually develop to be about 2' tall and will produce flowers much later in the summer.
Here we have the same type of Scabiosa that was direct seeded the previous November. This plant is about 3' tall and has already has about 20 flower buds on it. This photo was taken at the same time as the Scabiosa above.