Peer reviewing effectively and efficiently. The biggest take-home for me was that beyond 3 hours spent on a review, a review doesn’t improve. 2 hours is about the right amount of time.
The other nice bit of advice was to look for the message and claim in the abstract, then look for it again in the introduction, evidence for it in the results, and see if it is in the conclusion. If it is missing from any of those, probably there are problems.