[SQWIBB]

I pick by feel, nice and firm, best to pick before ripe. I try to go by shine vs. dull on black beauties but that isn't always accurate. The general rule is to pick before they lose their shine and get dull.
The longer you leave them on the plant the larger and more seeds you will have. Once picked, try to cook in three days.
If they start to get spongey, pick and cook right away.