Here's some:
Procrastination. Not much point in having a telephone and a list of companies to ring, then not doing it "because it's nearly lunchtime/going home time/too early (delete as applicable).
Sunday is just another day. If a client asks you to do something, don't say "on Monday".
Accounts. Never let it slip - if you've got spare time, make sure they're hunkydory. This can really pay off in January and June.
Pleading ignorance. Even if you are innocent of a cock-up find out what went wrong swiftly, making excuses will kill the account stone dead.
I could spend all afternoon on this, how many more would you like? We could fill several libraries with business mistakes!
