Here’s a great article listing seven “deadly” marketing mistakes that small businesses make from the clever people at Manta –
7 Deadly Marketing Mistakes Small Businesses Make. Their seven are as follows:

1. Failure to write a powerful headline
2. Absence of an irresistible offer.
3. A weak or non-existent call to action.
4. An inadequate list.
5. Relying on one marketing message.
6. Failure to measure campaign effectiveness
7. Not communicating with your current customers.

I would add this as #8, although I really think it ought to be #1, so we’ll make it #1A:

• #1A Not making marketing part of your regular routine

All too often I hear from small business owners that they only get a chance to market their companies when they are quiet, otherwise they are just too darn busy! The problem with this is, of course, that if you only market when you are quiet then it’s probably too late! The time to market is when you are busy or ticking-over nicely because then you’ll be generating a steady stream of interest which will hopefully reduce the quiet times. Forget ABC (Always Be Closing) and think about ABM – Always Be Marketing!