Larry David famously instituted a policy of "no hugging, no learning," meaning that the show must avoid sentimentality and moral lessons, and the characters must never learn or grow from their wrongdoings.
As Kramer (Michael Richards) became more popular, his entrance applause grew so prolonged that the cast complained it was ruining the pacing of their scenes. Directors subsequently asked the audience not to applaud so much when Kramer entered.
A running gag in the show is that Jerry (Jerry Seinfeld) can't act. This was actually a real concern for the show's producers. To weigh up for this, they needed strong supporting actors and actresses, hence Jason Alexander, who previously had been on Broadway.
Larry David was quite volatile in meetings with NBC executives, and would often outright refuse to accept their notes and suggestions. He was eventually banned from attending the meetings.
Jerry Seinfeld turned down an offer from NBC that would have made him $110 million for a tenth season of the show.