Right now is the time to plant your vegetable seedlings, but the trick is to know where to plant them and how to prepare the soil for their future and for your future salads. So, do not plant the seeds outside yet because when they germinate one cold morning could wipe them out even if you cover them.
The trick with vegetable seeds is to start them first in a plastic nursery tray. Fill the tray with a good, well drained, packaged soil. Keep it moist and not soggy wet. When distributing the seeds, sprinkle them as evenly as you can over the entire top of the tray. Minimally, cover them with your soil mix by holding your hands together with soil and slowly allowing it to barley cover the seed. Distribute any thicker clumps of soil to even it out and water very lightly holding your hand over the water, so as to not create erosion.
Place the tray in the sun where it receives early morning sunlight but also afternoon shade. If temperatures even dip into the low 40s, bring the trays into the house for the night. Most seeds will germinate in 7-14 days, some even less than that. Once the seeds are up a few inches, you can separate them with a Popsicle stick and either place them into little pots or directly into your garden, assuming all danger of frost is over.