One of the big pieces of advice is to avoid falling back on easy (and often inaccurate) stereotypes as much as possible. As memorable as Jack Nicholson's advice on writing women is - a man minus reason and accountability - it's a formula based on thin (not to mention sexist) stereotypes that leaves your characters flat and cartoonish. As a reader, it's a mood killer. As an author, I mentally try to tune in to the voice of the character (inner and outer) to get a sense of their personality, and allow that to guide their behavior. Usually it's a modified extension of my own voice, but relying more on the feminine side of my personality - not that I'm trans, but we all have male and female aspects of our personalities according to Carl Jung and other old-school psychiatrists. If I can't hear their voice clearly, or don't believe in it, then I can't write them realistically.
I read one story recently where the female protagonist is admiring herself in a mirror (yeah that cliche), and claims to have "the sexiest ass ever!" Fucking hell! EVER! I stopped reading right there. First of all, it takes a pretty self-obsessed character to spend that much time staring at their body in a mirror for no other purpose than to look at it. When they do, it's usually with more ciritcality than admiration - "Is that a pimple?" "Do my thighs still look okay?" "Am I getting fat?" "Are my breasts too asymmetical?" We (people in general) are far more attentive to our shortcomings than the positive aspects of ourselves. It's just basic human nature, and that encompasses women as well as men. Even if there are parts of their body that they're proud of, it might be "Well, at least my ass still looks good," but I doubt anyone thinks to themselves, "I have the sexiest ass ever!" A guy might say that if he was bragging about some hot chick he banged, but I doubt most women (or men) would have that thought about themselves.
What was happening was that the author was trying too hard to write from a female perspective, but their concept of femininity was based on bullshit Hollywood (and/or porn) tropes and cliches. The truth is, women - most of them - are not unreasonable, nor unaccountable, nor superficial, nor self-obsessed narcissists, nor emotionally volatile neurotics. We see these cheap archetypes over and over again, and they've always been laughable caricatures, not realistic portrayals. So try to make them feminine, but don't try too hard to make them very different from yourself that they become these outlandish alien creatures.