To begin. . .
1) Recent trends are to "deny all" via white-listing, than make exceptions for those visitors you desire.
a) whether based upon User-Agent, request, IP range, header, or any combination of the aforementioned four.
b) I'm not aware of (with only a few exceptions) of any "complete" examples in providing the coding for white-listing. Were these examples made public, than it would be an easy task for all the harvesters, and bad bots to circumvent the coding.
2) Before white-listing, the previous trends were in "black-listing" (denying after-the-fact based upon either your record of activity or record provided by another).
How do you recognize bat bots?
1) You review and analyze your raw visitor logs.
a) This requires and awareness of your website (s) layout, pages and how regular visitors interact with the pages of your website.
b) the capability to examine IP ranges and User-Agents.
c) I'm not aware of any website which provides examples and explanations of criteria to interpret the traffic of website, at least with a method of determining what is good or bad. Every website (or webmaster) has different goals for their site (s), and as a result, each must determine individually, what is beneficial or detrimental to their own site (s).
How do you block bat bots?
There are too many examples across the entire internet (not just here at Webmaster World), however not are current (recent activity or updated).
In addition and considering the www-as-a-whole, some websites are providing solutions which are inefficient, even inaccurate.
Here's a very old (note 2001 date) and long thread at Webmaster World; Close to Perfect
[webmasterworld.com]. In addition many of the lines were provided inaccurately by people seeking solutions, as a result, GREAT CARE should be taken (no blind copying and pasting) before any of the methods or lines are implemented.
prefer a reference to a current, highly regarded method
No such example exists!
Suggest you review the Forum Library, near top of page, as well as the two leading threads at page top.