I know firsthand just how annoying lag can be especially for casters that depend on mobility during every little fight. If you're new like myself and have been experiencing lag issues, such as clicking and your character struggling to get to that point (moving but warping back to a previous position, sometimes not responding at all, etc.), I might know how to fix this without the use of apps like WTFast and Lowerping (these options might be the best fix for some players, but in case you have tried these options and have not seen any significant improvement, keep reading).
Keep in mind that this method is not a guaranteed fix to your particular problem because there are so many possible culprits when it comes to lag.
If you have exhausted all other options to fix your lag issues, you have nothing to lose by trying this one (it worked for me when nothing else did).
There are two simple steps:
1. Make sure RO is allowed by your firewall.
2. You will want to port forward RO 20, 21, 80, 443, 4500, and 6900 (you will want to forward ALL of these just to be safe, and it won't hurt you in any way and is completely safe, it may even prevent future problems with the client).
If you are unsure of what you are doing and need assistance with port forwarding let me know in this thread and I'll write a guide on this post.