1.  Copy is there to sell.  The best reads as if you were there in person, talking with the customer.

2.  That means using simple, believable words.

3.  And it means putting those words in the right order.  Selling is a sequential process so first you must grab the reader's attention.  Then get them a little bit interested.  Next lead them to really, really want it.  Only then do you ask for the sale.  This process is often known as the AIDA model - Attention, Interest, Desire, Action.)

4.  Words that sell include You, Free, New, Best, Now, Hurry, Magical,  Fabulous.  The most powerful of all of these is Free, and the least powerful is any fabulous, magical word that gets overused, especially if it's given a magical, fabulous exclamation mark!

5. Poor copy talks about the product or service.  (eg:  Our Biggest Ever Catalogue - a feature). Good copy talks about what the product or service can do for the customer.  (eg:  Your Best Ever Choice - a benefit). 

6. Adopt an active tone of voice, rather than a passive one.  "You will receive" is better than "You can order".

7. Planning is key.  Know everything you can about the product or service.  Understand intimately the potential customer - what they like, who they are, what makes them tick.  Imagine their objections.   Only then is it possible to find the most motivating benefit, and put it across in a compelling way.

8.  Be clear about the purpose. Why is it being written?  What should it achieve?  What should the reader think, feel and do? 

9.  The best copy reads like it was written for a single person, not an anonymous, amorphous group known as the target audience.

10. Good copy is easy to judge.  Does it sell?