Use Sony Vegas Pro for the best editing results.
Make it look like you don't give a shit about loot, just laugh whenever you kill someone
Don't make an introduction with you saying things through runescape, instead use Sony Vegas Pro
Show your CB and stats quickly before the Pk vid starts, or mention it in the intro
Only keep vids where it's a quick kill, or where it shows the end of the kill.
Make the music in sync with the hits you do.
Only show yourself dying if yourr opponent dies too
Have a few jokes or silly things in runescape that might make the audience more interested in your vid
Have a good username (Spartaculus, etc.)
Use only the best weapons
Pures are always more fun to watch, unless the main is epic.
Play fair, unless your video is made specifically for tricking or luring.
Don't PJ in the vid
Say GF at the end of every fight or lol if the person PJ's you
Keep the video going, never have a slow part that bores the audience.
Hope these help,
WetRain