First, prepare your soil. I like to add manure to the soil to provide nitrogen for healthy growth. Add manure as soon as you can work the soil in the spring (at least two weeks prior to planting the lettuce).
Plant seeds in full sun 1/8 inch deep in rows, 6 inches apart. If you plant new seed every two weeks you can have lettuce all summer.
However, for mid-summer yield you must protect the lettuce from summer heat. As the weather warms, begin planting in partial shade, somewhere where the afternoon sun will be blocked by the house, garage or tree. If you have taller plants nearby, such as corn, sunflower, etc., put the lettuce in the shade of those plants.
Avoid getting the leaves wet when you water. This invites disease. Water the soil at the base of the plant till moist, but not soaked.
Lettuce does not compete well with weeds or pests. Keep the weeds pulled and hand pick pests off the leaves. I would not use poisonous insecticides on my lettuce. If you must spray, use insecticidal soap.
The biggest enemy of lettuce in the garden is slugs and snails. They can practically destroy lettuce in about two nights. The best method to eliminate slugs is to go out in the garden, every morning, at sunrise and hand pick them. Look in damp, shady areas and you will find them easily.
Do this until you can not find any more. You can also help eliminate slugs by removing any article in or near your garden that provides a home for them. Slugs love to hide under old grass clippings, wood, cardboard or anything else that gives protection from the sun. So, clear your garden of all of these items
You can also buy snail bait at the garden shop that works well. However, I urge you to use the “Pet Safe” baits that are now available.
The older (cheaper) baits are poison to you and pets. I would never put something that will kill pets on a vegetable I intend to eat.
You have the basic tips, now read the article on transplanting to see the proper way to get your lettuce in the garden.