In any sales situation, the closer is always the most crucial part.   This is very true with sales letters, in particular, as all the work you've put in preparing the prospect for the pitch will be put to waste if you fail to spur them into action.

Remember, once the reader closes the website or puts down the letter, there is little chance they'll read through it again (no matter how well your writing software helped you shape it).  As such, you want to spur them into action before they get the opportunity to either change their minds, develop more questions or forget about the pitch altogether.  Any heat that your sales letter generates will likely cool down if you let that happen.

Give Them A Clear Action To Take. Should the reader call a number now, set up an appointment within the next 15 minutes or enter their email to get the free report?  Whatever the action you want them to take, make it clear.  You do this by stating it in no uncertain terms, clad in big, bold letters.

Stick To One; Two At Most. If you offer five different paths of action for the reader, guess what will happen?  They'll usually end up spending the next couple of hours trying to decide what to do.  That's why you only leave them with one action (or two at most) - it keeps things simple.

Make The Action Easy. The easier the action, the more likely you'll get the sale.  Make sure you communicate this same ease with the way you word the instruction.  Saying "Call up the marketing department and look for either Miranda, Jason or Chris" is way more complicated than "Call us now and speak with one of our marketing reps."

Give It An Expiration Date. You have to give them a specific time and date for the action, whenever possible.  Telling them to send a text message in the next five hours makes the matter more pressing than not giving any time limit.

Give Them A Reason To Act Immediately. Why must I buy now when I can buy tomorrow?  Give the reader an incentive to perform the action immediately. Not only does it encourage them to act sooner, but it ends your pitch on a service-oriented note.