@Abc and other people complaining or generally experiencing lagg, or difficulties with the game RuneScape recently, Jagex has Announced twice that the game is having many difficulties but these difficulties vary from place to place or user to user, the engine will have yet another bug update soon that will fix or hopefully fix most of these bugs.
Super on-topic- I doubt you need to do anything more for RuneScape than not be downloading a bunch of things and make sure you use your disk cleanup every two weeks. other than that if your lagging or having difficulties I would suggest if you have a desktop open your computer brain (tower) and make sure there aren't any cobwebs or dust buildup and if there is make sure to carefully and well instructed by a manual or by common knowledge remove the motherboard and be sure to clean the plate underneath it.
If you have a laptop unplug the battery and look into the two sockets(plug-ins) and make sure there aren't any bugs or dust/cobweb build-up.
Also a nice Disk De-fragmentation overnight is always good once a month.
as to how to prioritize your pc for gaming, make sure you set your visuals to the bare minimum(best performance setting in computer properties>advanced settings) and allocate a fair amount of RAM to your game you are currently playing, I have forgeten the universal coding for this but I believe Game Booster Pro does this automatically for many games.
~Blaze