Now that you've got the basics down I think you're correct in looking towards the more specialized scenarios - handling CC / DPS on different targets at the same time or reacting to certain events (movement or otherwise) and so forth.

/click macros are very useful for squeezing out as much DPS as possible while spamming a single key and they also allow for inserting specific targeting logic after the assist but before the spell is fired.

The way I delved into those tasks was to get my normal farming done for the day and then head for one of the harder (for me at the time) dungeons and start pondering what it was about a given encounter that was proving difficult and working out ways to tackle that difficulty.