Playing RDM with a high ping does suck but it's worse when you have the ping spikes because the flow of dualcast is tampered with. If you're able to use a wired connection then do it as spikes will happen over wireless. Look into Internet Over Power connections if you don't want to run a cable from your router to your PC. I've done this and it's a big help.
RDM is a very simple class to learn and master. Use a short casttime spell first then follow with a longer casttime spell all whilst keeping your mana even.
For single target: Jolt-> Verthunder/veraero. If Verfire/Verstone procs use that instead of Jolt.
For AoE: Veraero II/ Verthunder II -> Scatter.

Once you have that pattern down with dualcast you also gain a lot of movability.