This is a fun one! Martin's #2 is my favourite so far, but here goes:
1. Where there's life there's phlegm
2. You can't make an omelette without a frying pan
3. Don't judge an e-book by its cover
4. Those who sleep with dogs get a criminal record
5. Too many cooks cook too many
6. The course of true love is downhill
7. The best-laid plans of mice are seldom impressive
8. Say 'ouch' while the iron is hot
9. It's no use locking the stable door if you don't have a stable
10. Don't wash your dirty linen in the sewer
I'm sure some of those must be old jokes, but I couldn't find them on google. Apologies to anyone I inadvertently ripped off.