If your on a main you should try your hand at some bosses, or go to GWD. If your skills are high enough, the possibilities are endless Some of the grandmaster quests might be alot of fun too
I suggest getting into hybridding. There's some good guides on youtube, but it relies heavily on how fast you can switch between outfits. If you don't manage to hybrid, I suggest you dharok pk. It's fun, but it's much more fun with the fact that you can VERY easily make money.
Yeah, I think you could have the most possible fun if you went monster hunting and took on all the hardest and most rewarding monsters in the game. You could hunt Revenants in the wilderness, go kill Tormented Demons in hopes of getting a few dragon claw drops, kill all the bosses in GWD, take some friends to waterbirth and attempt the Daggannoth Kings, go fight the Chaos Elemental, hunt Frost dragons (make some cash collecting frost bones and if your lucky; a visage!), Mithril dragons (chance of getting a dragon full helm), maybe even gather a great team together once you get your chops up and attempt to kill Nex (the highest level boss in the entire game, with some of the most expensive drops in RS).
That is what I would do. Just enjoy being a high levelled main and having very little restrictions in the possibilities in your gameplay.
Well you're gonna need to be 80+ in mining, hunter, fishing, and woodcutting.
It would also be very helpful if you had 80+ smithing, crafting, and hunter.
Summoning is not so important, but you should have 80+ defense, magic, or range.
Then just make armour corresponding to your favorite attack style, and go rape some noobs. SS helps a lot.