Lemons should be heavy for their size and have smooth, thin and firm skin. Avoid soft, spongy lemons with a wrinkled or bumpy skin - they’re bound to have less juice. And the smaller, the juicier.
Lemons are juicier if kept at room temperature, and they’ll stay fresh for up to two weeks. They’ll keep for three to four weeks if loosely wrapped in plastic and stored in the refrigerator’s crisper drawer.