The punctuation fanatic will put a couple here:
A Guide to Proper Comma Use - https://www.businessinsider.com/a-guide-to-proper-comma-use-2013-9 - An almost too-limiting technical viewpoint on commas, but an excellent starting point.
Rules for Comma Usage - https://guidetogrammar.org/grammar/commas.htm - Broader comma coverage.
Using Semicolons - http://writing2.richmond.edu/writing/wweb/semicolon.html - A short and to the point discussion of semicolons.
And a topic about which I've annoyed more than one person:
Lay or Lie? - http://englishplus.com/grammar/00000233.htm - A succinct outline of the subject without all of the usual excess that simply makes it more confusing.
Set or Sit? - http://englishplus.com/grammar/00000250.htm - An outline of how to use the two verbs, another problematic pair.