I've watched Angel and Buffy separately and in tandem.

It's a bit of a bugger to get right.

There are some guides out there about which episode of which to watch when and there are a few moments that don't quite fit but it can be fun trying to slot the pieces together (Wikipedia has a nice list).

Neither show is really about vampires (they have vampires in them as well as demons, werewolves, cyborgs... but not leprechauns) they are more about a much more frightening group of creatures, youngsters (particularly the female of the species), what they do, how they grow and the trials that beset them.

The monsters are metaphors...do you see?