Slime spray is very easy to avoid. You don't have to be completely out of in front of him. It's like a 45-90 degree cone. We just basically scatter around the boss instead of having fixated positions. If the boss turns in your direction you have to move a step or two depending on if he was targeting you or the person next to you. Think of it like a clock face. If you have the raid split into 12 groups around the boss and the boss looks at 2 o'clock to cast... 2 o'clock people need to move to either 12 or 4 (at least 2 away) while 1 and 3 people need to move only 1 away. Now only 1 quarter of your raid has to move instead of half of it. People who typically do better on DPS for this fight actually minimize their movement, if they only have to take one step, they will take one and resume their role.
"In anything, if you want to go from just a beginner to a pro, you need a montage." /w TankSpot WTB Montage for Raiders.