I live in the Salinas-Monterey area where a lot of lettuce is grown, lots & lots! Varieties like butter, romaine, iceburg, boston & red are what we commonly find in the local markets. I would say that most of the lettuce in this country's supermarkets are from this area.
Anyway, the temperature around here is mild (averages around 70 degrees). Lettuce doesn't like really hot weather so that would be my number one tip. If your summers are really hot you might try to grow yours when most of your really hot weather is done. Keep the soil moist, too....good luck!