How do I figure out exactly what I need to study, and what questions to ask myself?

[Amit Dutta]

Jumping in here. Sounds like a plan, but you might also consider this. Start on your illustration, choose and do your value studies in order to directly apply to the piece. That way your study is tailored towards something specific and not just for it's own sake.
Eg if you know it will have a misty setting study values from various reference related to mist. This can apply to every and any aspect of your painting.

good luck!