You can try completing certain quests or participating in specific events related to it. Sometimes, rare drops from monsters might also give you a chance to obtain it.
One good order could be starting with the Tutorial Island quests as they introduce the basic mechanics. Then move on to the Lumbridge quests which are relatively easy and build a foundation. After that, quests like the Vampire Slayer quest can be a good next step as it has an interesting story and unlocks some useful items and areas.
I'm afraid I can't tell you the author of 'a deadman's cross novel'. There's no information available to me at the moment. It could be a local author from a particular region or a niche writer who focuses on a specific genre related to the theme of the deadman's cross.
Well, without having read the 'a deadman's cross novel', it could potentially be a horror - themed story. Maybe the deadman's cross has some sort of curse on it, and the characters in the novel are either trying to break the curse or are being haunted by it. It might also be set in a spooky, desolate location where the cross is found.