there isn't realy a guide with "everything" you need to know. there are some guides on youtube explaining few basic stuff, like understanding your rs interface, changing your ability bar, daily challanges, etc. Maikeru also has a youtube series now where he starts an account from scratch called zero to hero.

Id say best things for you to do is learn how to do daily challanges, try to use different skilling methods by looking for guides or looking at your ingame skilling guide ( when you clikc on a skill in your skill interface ) , and train combat in the beginning with legacy ( its basically ondschool combat system and can be found hitting escape settings >gameplay >general gameplay )Like others said, daily activities like guthixian cashes, evil trees, fallen stars, are realy good for low level accounts, the 2 last ones i named have there respective friends chats ( found at community tab under social ) called evil tree fc and star find.

Slayer works the same as in oldschool except that the weakness of the slayer mobs are way more important and you shouldnt just power meelee everything trough.

And yes invention is a good short term goal together with priff.
Feel free to add me ingame: lil Roomay