This one needs little intro aside from the fact that I'm calculating and manually typing yesterday's date far too often. Here's a simple and handy tip to insert yesterday's date using TextExpander. Make a new snippet, give it an abbreviation of 'yesterdate' and include the following for the snippet.
%@-1D%e %B %Y
This seems like a super-obvious tip (and it absolutely is), but I've only instituted it today and it would have been very handy for me over the last few YEARS. Hope it helps someone else.
As a lightweight bonus (and an even more obvious tip) use the abbreviation 'todate' to insert today's date. (Replacing 'day' for 'date' in each of the abbreviations works for me...and remembering what I've named my snippets is one of my biggest struggles!). Anyhow, the snippet code for today's date, is just:
%e %B %Y