I thought this was quite a given way to do it but John seemed surprised by it when he saw me doing it once so I’ll document it here in case he’s not the only one who hasn’t thought of it yet:

When checking through your spam folder for false positives, sort by the Subject rather than the date or whatever – you can then instantly eliminate huge groups of the messages that have the same subject line or that all start with the word ‘Viagra’ etc. Makes it a lot easier to browse through and find those pesky real mails.