okay, first thing you gotta do,
work out what part your at, if its the slaying of the dragon then just take best food you can, best armour you have, maybe green d'hide legs and go in there and just slay him !
the rewards are definetly worth it,
on completion you will recieve alot of exp and the chance to wear green dhide top and rune platebody !
these are great as very powerful armour and best in f2p game !
hope i helped you out