For example, most people (of both genders including B’nei Torah) think that if you have a Haetz and a Haadamah, you make the bracha on the Haetz first, and this is incorrect according to the Mishna Berurah and most comtemporary Poskim.
It is better to make Haetz first. This is the opinion of the Behag, although it says in Shulchan Aruch OC 211 that you can pick which one to eat first, but the minhag is not like the Shulchan Aruch.