Checking the Engine

I was hoping to check:
-MAF
-Spark Plugs
-Cam sensors
(02 sensors were on my list but my friend told me that its a pain, and if something was wrong with them the CEL would be on.)
Why am I doing this? Well, I still have issues with the MPG, and just for the hell of it, I want to start learning. (Yes I'm a n00b.
)There's no CEL if anyone was wondering.
I do not know if the dealership did that one recall on that hose.
I already replaced the air filter.
I'm thinking about getting new spark plugs. NGK Iridiums.
Any tips, or suggestions are appreciated.


