Don't try to teach your Grandma to suck eggs
Don't offer advice to someone who has more experience than oneself.
These days this proverbial saying has little impact as few people have any direct experience of sucking eggs - grandmothers included. It is quite an old phrase and is included in John Stevens' translation of Quevedo's Comical Works, 1707:
"You would have me teach my Grandame to suck Eggs."
The notion of advising the young not to offer advice to those who are older and more experienced wasn't new even then. Nicholas Udall, the author of 'Ralph Roister Doister' the first regular English comedy, and the headmaster of Eton, translated The Apophthegmata in 1542 from the works of Erasmus. That includes:
"A swyne to teach Minerua, was a prouerbe, for which we sai: Englyshe to teach our dame to spyne."
The idea was carried forward to the 20th century with this quotation, attributed by The Reader's Digest to Mark Twain (although not proven to be authentic):
"When I was a boy of fourteen, my father was so ignorant I could hardly stand to have the old man around. But when I got to be twenty-one, I was astonished at how much the old man had learned in seven years."
See also: the List of Proverbs.