Oddly enough, there seem to be a few simple rules to the shows. Remember these as you watch an episode because they follow through almost every time.
Rules of Buffy
1) If someone draws Buffy's attention away from Willow, they're bad.
2) If someone's wanting to have sex with Xander, they are or once were evil.
3) If Buffy is trying to fit in with someone, it won't work.
4) If Giles gets a girlfriend, it's doomed.
5) If someone at some point in the episode is upset, then you're on the right channel.
Rules of Angel
1) If Cordelia doesn't say something tactless & potentially hurtful during an episode, than the writer just forgot to put her in character.
2) If Angel isn't out to save some some woman, you're on the wrong channel.
3) The name of the game is sexual tension.
4) If someone comes looking for Angel because they've heard of him & want him on a case, they are tricking him in some way & have an alterior motive.
5) If you've got something to redeem for, or are otherwise lost in some way, come to L.A. But remember, mostly, you have to save yourself.