Teach your grandmother to suck eggs
Usually expressed in the negative form of don’t teach or try to teach your grandmother to suck eggs meaning do not offer advice to people who have more knowledge and experience than you do. It dates from the early 18th century. Sucking eggs, however, is not to be taken literally. A suck-egg was a fool or an idiot and dates from the early 1600s, an expression that is largely obsolete these days. Thus, the expression simply means, do not take your grandmother for a fool. Before the expression came into vogue in the early 18th century, there were several earlier versions of the same concept, such as do not teach your dame to spin, which dates from the 1500s.