Copywriting for PPC is particularly challenging, especially for marketers whose previous experience is in print, in those massively long online sales letter sites or who generally have writers diarrhea, like yours truly. Even the pro marketers in this field admit that trying to explain the value proposition of your product over a competitors' in a few lines is a tough task - and the lines that work one month may not the next. Here's a few tips I've gleaned over the years that also appear to have general consensus among other marketers.

• Use powerful adjectives such as 'unique', 'cheapest' or 'incredible'
• Be specific, instead of 'fast delivery', user terms like '24hr delivery'. A 'limited offer' could be 'ends X' date to help create a sense of urgency.
• Mention the price if possible; it helps to ensure that you have more pre-qualified clicks and is especially enticing if your pricing is good.
• A few colleagues believe that the Capitalization of Most Words is a good strategy. Personally, I'm not convinced on that one. I think it's distracting rather than enticing when applied to multiple words; and I believe that some ad networks don't allow it.
• Check out the wording all your competition is using in PPC ads, if they are all doing the same thing, try to be different.
• Stock a famous brand? Mention it.
• Eye tracking studies have shown that the title line in a PPC ad is the element most read, so use the exact search phrase you're targeting as the title phrase; except if everyone is doing the same. This is so that the searcher can make a direct connection between what they want, as expressed in the search query - and what you are offering.

Of course, if you have a stack of terms you are targeting, the last tip may not be practical, so perhaps reserve these custom title ads for the less common terms that people use when searching. For example, instead of just having a title of 'shopping cart software' to match that term you are targeting - try 'PHP shopping cart software' to match that term.

You certainly don't get much time or space to make a good impression with a PPC ad; devise the perfect system and the world will beat (click) a path to your door - and hopefully bring their cash too. Don't forget; the best PPC ad in the world will do little for you if the click leads to a landing page that's not up to the task and converting that visitor to a buyer.