I am always amazed that perhaps only 1 in 50 Founders interview their potential angel investors or VCs properly. This is a two-way deal. 

Here are a bunch of questions you should ask. 

how many investments has the firm/angel done in the last six months?

[and if a VC firm or angel network] how many have you yourself lead internally in the last 6 months?

…and are you currently investing today? if YES what cheque size?

are there any terms or costs or quirks i should know about that deviate outside of industry norms for this deal size? e.g. if they split legal costs, no interest charges etc

when were the last 3, how much, what were they, what % did they take

do you make your own decision to invest or do you wait for other investors to invest first and follow? * see footnote

[and if a VC firm or angel network] who makes the decision in the fund?

[and if a VC firm or angel network] is there an investment committee, when does it meet?

where does most of your dealflow come from?

what is your follow on cheque size, how many of your portfolio have they followed on to and how many do you expect to?

how long did the last investment take from first contact to money in bank?

[if you are raising on a note] when was the last investment you did on a convertible note?

[and if a VC firm or angel network] who do you view as your nearest competitor?

[if an angel] who do you really admire as an angel investor, and why?

[if a VC] which other VC firm do you really admire/which partners, and why?

[if a VC firm or angel group] who is the senior partner in your firm who knows this sector best?

what are the metrics you are looking at in this particular sector?**

..and does he or she have the authority to make the decision to invest?

what are the next steps from your POV?

what value can you [and your firm] add to our business over the next year?

These should be asked in the first meeting or call. 

And if the call is with a VC firm's Associate, use this initial call to keep the bulk of the focus on them, after of course doing an enthralling but brief sell of your own proposition. This decreases an Associates success in data-mining your business for their market database or — occasionally — them doing DD prior to a competitor investment. At the end of the call ask when you can have a meeting with the General Partner they mentioned earlier.