One of the most prominent tenants of /r/theredpill is that "a woman can never tell a man how to attract women, only a sexually successful man can." It's the fisherman's analogy: would you ask a fish how to catch a fish or a fisherman? One of the arguments behind this tenant is that woman give shitty advice, the shittiest of which is "just be yourself." To be fair, one could argue that "just be yourself" is shitty advice. You've always been yourself, and it sure as shit hasn't worked nearly as well as you'd hope.

However, I believe that many, including people over at /r/theredpill, take "just be yourself" too literally. They take it to mean "change literally nothing about yourself at all whatsoever and I'm sure you'll meet the woman of your dreams." Some go as far as to accuse women of purposefully giving this awful advice to beta men in order to keep them from bettering themselves lest they accidently hook up with an "unnatural" alpha. Others simply believe women are ignorant to the plight of a "low SMV" man, since any women (above a HB5) can get laid by doing nothing except existing (or just being themselves).

Regardless, "just be yourself" isn't a literal "change literally nothing about yourself at all whatsoever." It simply means "be the best version of yourself without lying about who you are." One can work out, buy a better-fitting wardrobe, pick up an interesting hoppy or two, and as a result have better sexual success all while still being themselves. It's about being true to yourself, owning your quirks and/or more unusual hobbies, and making the effort to physically and mentally better yourself. The problem is that can be difficult, and people would rather just find a shortcut and lie about (or to) themselves. Nobody wants to hook up with, fuck, date, or marry somebody who's a fake. That's what "just be yourself" is about. Self-improvement and "just be(ing) yourself" are not mutually exclusive in the slightest.

Disclaimer: obviously this isn't universal. If you're a racist, sexist, anti-theist, religious bigot, misogynist, misandrist, et cetera (for example), then being the best version of that is probably shitty advice.

TL;DR: "Just be yourself," when taken to its logical conclusion (as opposed to being taken 100% literally), actually means "be the best version of yourself without lying about who you are." Socially, romantically, and sexually, this is pretty solid advice.