- Update your Java to the latest version.
- Try tinkering with your RS settings till you get a higher FPS.
- Update your graphics drivers to the latest version.
- Do a disk clean up + disk defrag.
- Try running through the RS Client as some say they receive slightly less lag through that.
Ultimately, it's the game that is causing the lag, Jagex have stated that this should be fixed soon.
Just clicked this hoping it could help me out, but I just tried something that worked for me to improve lag a bit. I already had custom setup with everything to the lowest it could go, but I switched my display option to OpenGL and it helped. You should try out all the available display options.
Laptop really summed up all the current working methods. The only way I've been able to get the game running anywhere near as smoothly as it did Pre Bot-Nuke is putting the Graphics settings to the lowest possible. Even then, it lagged a bit.
Jagex have stated it will be fixed though, I believe when they release 'Optimus,' their second Bot Nuke. Rumours say it's going to be released sooner rather than later.
Try Gamebooster
Use lowest details
Update your graphic card drivers
Also heres a method that is unknown but is working good.
Check how much RAM your computer has and since Runescape only assigns a low amount of ram (256) then you can increase it by looking for the file "runescape.prm" then the third bullet point should say something like "Xmx256m" which you can edit it to make Runescape use more RAM. For me mine is set to "Xmx1024m" with 8GB of RAM. It should increase your FPS by a bit atleast.
Make sure to check the Runescape Official Forums in the Support section if you have any more questions. There are multiple threads there with solutions.