This is a big request, but I'll throw it out there anyway.
Having some sort of writeup like this:
https://en.bitcoin.it/wiki/Protocol_rulesbut for the process of creating a new transaction could be useful.
It seems like there are a few pitfalls to be aware of with fees, selecting coins, etc.
But it's not a protocol rule (well, maximum txn size is I guess but thats already there)... this is more an issue of common norms on the network today, enforced by peers sure but its not part of the distributed algorithm, nodes can and do disagree on it and it doesn't fork bitcoin.
Perhaps best practices should be described there, but just like the protocol rules don't tell you not to perform undefined operations in C I don't know that these other recommendations belong there.