in order of relative easiness, easiest being first:
GTB - crystal arrows
Eddga - crystal arrows
Phreeoni - oridecon arrows
Garm - wind arrows
Stormy Knight - stone arrows
RSX - oridecon arrows
Dark Lord - silver arrows
GTB isn't diagonal doublestrafe, you can just snipe him over the water
for eddga's map, type /effect when you get there, this will keep the horongs from "hallucinating" you. Also, horongs dont take damage from arrows, so save yourself some time and crit/falcon them if you need to kill them.
if garm gets close to you, teleport immediately. he'll SG you or his mob will frost diver, and when you're frozen, you're dead.
stormy knight SG's also, so watch out, same story on him.
RSX and DL are tough because they're maps are not wide open, so they're hard to get into position sometimes.
forgot to add, poring MVP's are a good place to start.
deviling
angeling
ghostring
especially deviling, you can practice your diagonal DS technique on him, he's how i learned.
Edited by Astatine: Merged double post.