On 'the rules':
Again, just a fast look at VC finances shows that VC just MUST hit 'home runs' such as Dropbox or better.
Then just a fast look at the history of home runs shows that get only a few each decade. And just a fast look at those home runs shows that a significant pattern is super-tough to see. And, any such pattern has only a few examples because the larger 'circumstances' change so much from one decade to another. E.g., it used to be that a trillion bytes was a REALLY large chunk of hard disk space, but now it's not so large just as main memory.
So, since have to be looking for such home runs under such circumstances, what good 'rules' can be formulated? Remember, we're looking for home runs and not trying to find a description of a VCs average arriving e-mail pitch.
Or we're looking for some tiny number of golden needles in in a huge pile of hay so that statements about some average about the hay are just irrelevant.
Well, one could guess, 'the first rule of VC is that there are no rules', but, actually, that is too strong.
But not good is the rule against 'single founders'. Why? With the larger circumstances today, a single founder has some big advantages. I will let readers fill in some of the advantages based on current circumstances just as an exercise!
Next, for 'the rules', there still are some that can apply to some of the startup candidates, One collection of such candidates is based on startups where the core 'secret sauce' is especially powerful and can be evaluated just technically. For a biomedical analogy, consider a safe, effective, cheap single pill cure for any cancer: Then just evaluate the pill and f'get about the founder because if do have the pill and if he did invent it, then f'get everything else about him! He invented the pill, for god's sake! Or, we know you are plenty smart, but could you have invented that pill? So, if he's smarter than you, then you've just gotta think that he's plenty smart. I mean, given that he invented that pill, what are the chances he's a doofus? Or, to be quite specific, even worst case, just what issues of 'business acumen' couldn't be solved by hiring him a COO, CFO, SVP Operations, SVP HR? And there's no good reason to suspect such a worst case or even a bad case. Or, did I mention, the guy invented the pill?
For meaningful rules to apply to all IT startup candidates, that seems to be asking too much.
The simple answer that will fit on the back of the usual 3 x 5" card of VC rules that even a VC can understand is, in looking for the crucial home runs, the first rule is there are no rules.