respawn frags are very very useful, and not that difficult as the most guys think
you only have to know where your opponent respawns:
a good tip for this is to download and watch this movie
http://combowhores.freakzot.de/index.php?site=files&file=14
he does many respawn frags and you can learn many of his aggresive playstyle!
greetz
dude!