The first tip I have for planting peas is to pre soak them in water overnight or for about 12 hours. Why? You ask? Because the first step in the seed sprouting process is moisture absorption. Nothing can happen until the seed is sufficiently water logged. The seed starting process happens more rapidly in a cup of lukewarm water than outside in the cold ground. Presoaked seeds will usually sprout several days earlier than those not soaked.
Now for smaller seeds, like different varieties of lettuce, the seeds are so small, I don't bother soaking them. If you really wanted to, you could lay them out on a damp paper towel and then lay another damp paper towel on top of the seeds and keep it wet for 12 hours or so. I tried it once and it was more work than it was worth.
Here is a diagram of how to space your peas and spinach in the ground, in their individual square foot. See HERE for more info on Square Foot Gardening.
Now let's get to how deep to plant them. Peas needs to be placed about an 1 1/2 inches deep. I usually measure this by, sticking my pointer finger into the ground until the soil reaches my middle joint. (where your finger bends)
Here are the holes, ready for the seeds.
Here are the seeds in the holes.
Here they are covered with dirt and watered well. I usually pour some on and let it sink in and them pour some more.
Now I'll show you what I built to keep them warm. I got chicken wire and cut a piece about 18 inches long and bent each end down at about 3 inches like so: