Start by separating all your packets of seed into two piles: those that will be "direct-sown" (planted right in the garden) and those that will be started indoors.
If there's no information on the seed packet, start all your seeds about
6-8 weeks before you'll plant them outdoors. Make note of which plants
are too big or too small at planting time, and then you can make
adjustments next year based on your notes. Some seed should be planted directly outside in the ground. Like beans, sun flowers, peas, corn, radish do not like to be transplanted.
It helps to know how deep the roots are, so you can choose the right size pot to start them in. Like Peanuts have 12 in roots. I did them in new paper folded cups. The roots went thew and under the paper of the other cups. They did fine. But made it hard to take the paper off with out disrupting the roots.
I am in Zone 5 Missouri. My last frost date is April 15. With the weather changing so much. March was fine for potatoes to be outside. We had our last frost on April 2, 2015. So they had to be covered on that date.
I use the lunar signs to start seed so after the new moon in Jan, Feb and March, I start seeds.
The cold crop should be started first. Broccoli, Cabbage, Cauliflower, etc. Jan
Tomato and peppers are also one of the first ones to start. I prefer larger plants to transplant out doors. Feb, may be when I stat them. I will also start, true potato seed, (TPS) not tubers in Jan and Feb also. Last year it was March. I found they were to small in April.