it's best to direct sow

it's best to direct sow lettuce seeds in single rows or broadcast for wide row planting. If you broadcast (as the seeds are so tiny), you'll just thin to the right spacing. We like to take a row and just plant a square every 2 or 3 weeks so that we have a continual harvest

Lettuce seeds are so tiny and hard to collect, so we don't usually save this crop. If you wish to try, go for it!
1. Leave a plant or two to produce a
seed stalk.
2. After the plant blooms and the flower
forms a miniature “dandelion head,”
gather the seeds.
3. Separate the seeds from the chaff by
rubbing them with your fingers