SO many things, you may have done them already.
Yes weekly picking keeps plants young; never cutting their baby leaves, always removing outer leaves.
Spacing about 9 inches each way – closer spacing means they feel they are running out of room for roots and leaves, creates desire to go to seed.
Soil with enough organic matter to hold moisture and sufficient nutrients, as described elsewhere on the site.
The right varieties eg Salad Bowl goes to seed more quickly than the others I recommend.
Picking old and decaying leaves off to keep slugs less interested. Also all weeds.
And general good growing eg if close to a hedge which sucks moisture from soil, plants are stressed and then flower earlier.
Wishing you sucess!