aws logs tail /aws/lambda/my-function --followAdd --since 1h to start an hour back (10m and 2d work too), and --format short to drop the stream names. Filter for errors only:
aws logs tail /aws/lambda/my-function --follow --filter-pattern ERRORFind the log group's name when you've forgotten it:
aws logs describe-log-groups --query 'logGroups[].logGroupName' --output textThis replaced a lot of clicking around the console while I was debugging the Open Graph image Lambda.