When referring to Ross, Rachel says she doesn't go for guys right after they get divorced. Yet she had earlier pursued Joshua even though his divorce wasn't even final. Still, this may be a new rule for her because of what happened with Joshua.
When Rachel and Monica attend Danny's party they go downstairs and meet Danny in the hallway. While talking to Danny and his friend you can see the set for Monica's apartment behind them.
When Rachel tells Danny that she's going to a Regatta Gala, Danny asks her if she sails. She says no, but later in the series, Rachel teaches Joey to sail when he wins a sail boat at an auction, saying that her dad used to take her sailing all the time.
Monica assures the health inspector that she knows she is required to wear her chef's hat while in the restaurant kitchen, but she is shown hatless in multiple episodes.