Lemons should be firm to the touch, and bright yellow with a glossy shine. Coarse skinned and large lemons tend to be thick skinned, which means you'll get less juice from them. Heavier fruits with fine-grained skin are juiciest. Avoid hard, shriveled lemons - spongy, soft lemons - those with blemishes - or those that are greenish.
Lemons can normally be stored in an airy basket at room temperature for upto two weeks, however if you plan to keep them for longer period, store them in a plastic bag in a refrigerator crisper from the offset - they will keep for up to six weeks.