8) Gene Roddenberry banned stories about warfare with Romulans or Klingons. He also wanted no stories about Vulcans, whatsoever, according to the original March 1987 Writers/Directors Guide (PDF). Other standard tropes from the Original Series that Roddenberry banned from TNG: "stories about psi-forces or psychic powers," "swords and sorcery," "mad scientists, or stories in which technology is considered the villain." He also never wanted to see the crew violating the Prime Directive, or "toppling cultures that we don't approve of." And no stories in which the ship is put in danger because the technology fails, or the crew makes a dumb mistake.
The original series bible (which is a fascinating read), also says Picard and Riker have a "father-son relationship," and Picard often pretends to think France is "the only true civilization on Earth." Also, the phrase "fully functional" is underlined when discussing Data. And Tasha Yar is obsessed with Wesley Crusher, who's her "beau ideal" and the childhood friend she never had. Also, Picard "cannot help noticing that Beverly Crusher's natural walk resembles that of a striptease queen." Source: Original Bible.