Choose a cool site (eg in partial shade) to prevent the plants from bolting
Best planted in fertile, moisture-retentive soil or in containers filled with compost - you could plant 3-4 plants in a 40cm pot
Plant 15cm apart
Water lightly but often so that the soil is kept moist but not waterlogged.
As the stem elongates, the rosette formation of the leaves naturally changes to a small tuft of leaves on the top.
Mulching will help keep plants during hot, dry spells
Problems & Pests:
Slugs - protect celtuce from slugs and snails, especially while the plants are young
Discoloured yellow/brown patches on leaves - this is most likely to be a lack of water.
While the plant is young the outer leaves can be harvested for salads as you need them - after the stem starts to elongate and the rosette changed to a tuft of leaves, let it grow to 20-25cm before harvesting the stems.
Stems are best used within a few days (peel and slice them up and use them in stir fries)
You can keep celtuce in the fridge for several days