Vlookup,
Good for you for realizing and having the desire to round out those BA skills.
How are you documenting functional requirements today?
If you aren't already doing it, read through the Interview Questions that get posted here on a regular basis. There is a large list of them so far, and they are specifically written to get to the point fast. Great overview on a lot of different topics.
A basic understanding of Use Cases and UML can go a long way even if you don't plan to use them on a regular basis. Also Agile is another big topic that can be helpful. Use Cases are part of and support UML while User Stories are similar to use cases but briefer and part of Agile Analysis and Development.
I could probably dig up a book or two that would help in these areas.
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