***Warning: This is how I sow my garden. This method may or may not work for you. I am NOT saying that any other way is wrong. This is what works for ME. I am providing this information so that others can have a starting point for their garden. I do not guarantee that this will work or that you plants will grow.***
I started by digging out all of the weeds, and spreading manure. Next.....
Carve out your trenches. I free hand mine. I don't care it they are straight. They just need to be far enough apart that I can companion plant later on. My spinach needed to be 2-2 1/2 feet apart.
Drop you seeds in. I'm not precise when I drop them in. The spinach needed to be 6 inches apart. I dropped in 2-3 seeds every 6 inches. If I happen to have all of the seeds sprout I'll pull up whole plants and use them when I cook. That way they are thinned to the 6 inches apart they need to be and I don't waste any seeds. Next cover with soil. Only about 1/2 inch. I like my plants to be in valleys. That way the water stays with the plant instead of rolling down a hill.
Water well. 2 different reasons to water.
1. It helps compact the soil around the seed so that it doesn't rot in the ground.
2. Watering keeps the top soil where it belongs. If you happen to use a tiller you will notice that with strong winds that there is dust in the air. Well that is the top soil that has been tilled up. After all of the hard work I just put in I want my soil to stay where it belongs.
Good Luck with you Spinach and Happy Gardening!