First, if you've already proofread it recently, a second try will most likely not help. You won't see the typos and weird sentences anyway :) I'll advise to focus on specific short parts that can make a difference in the reading. It's also the right time to get someöne else on board to give these specific items a second look (with fresh eyes).
Without further ado, I suggest you limit yourself to checking the following items:
The main check here is not really for typos (although be sure to fix those you will see), but rather for clarity.
- General introduction, general conclusion
- Introduction and conclusion of each chapter
- Summary/abstract, if one is included (sometimes it's written in 10 minutes in a haze, in which case it's worth extra checking in the end)
- Acknowledgments, if it's already present (some people only include it after the defense is over). Make sure you're not forgetting someöne important, like your wife or your bonsai.
Figures and figure captions
- Quality of the graphics
- Do color and symbols mentionned in the caption match the figure?
- If you intend to have black and white figures in print, are the figures understandable in black and white? Do the captions make sense for both version (color and B&W)?
Check your equations. Again. Typos there are typically hard to find.
Numbers & tables
All tables, all inline numbers: make sure they include units, make sure the number of significant digits displayed is reasonable and consistent.
Do not care to much about the formatting: if most of it is okay, noöne will really complain about one or two missing page numbers or lack of italics in one title. However:
- If references are hyperlinked (using DOI number), click on each to check that they match the right online paper
- If a paper is “in press” or “accepted for publication” or something else, check if it has been published since and update its status
(The starting point for this was my answer to “Examining paper proofs”, but it is now significantly different)