You’ve got to get them to take action. There are a number of points to bear in mind when you’re trying to turn your reader into a customer.

Stand Out
You want to be sure that your reader doesn’t miss your call to action. It’s got to absolutely stand out from the rest of the page. You can do that by playing with font color, font size, underline, bold etc., but make sure it’s easily noticed so that it can be acted upon!

Be Clear
Orders rarely come in the form of long sentences. In general, marketing material should take the form of short paragraphs, punchy phrases, and bulleted points that spell out the benefits as clearly and quickly as possible. Potential customers tend to scan rather than read.
The easier you make it for them, the more likely they’ll buy from you.

Compel
The words you use to persuade someone to take action are crucial. You want your call to action to include real action-packed verbs that are simple to obey. Use phrases like “Click here”, for example, or “Press Submit”. The more precise the verb, the easier it will be for the reader to take the action you intend.

Play it Straight
Once you’ve got them doing what you want, you don’t want to waste time. If you’ve told them to click on a link so that they can fill in an order form, make sure that the link leads right to the form. Don’t give them a chance to change their mind. Even the best call to action copy only works for a short time.

Create a Sense of Urgency
Many people like to put off making a decision as long as possible, especially if that decision means spending money. The fact is though, if they don’t take action as soon as they finish reading the email, they probably won’t take action at all.

You have to create a real sense of urgency, an idea that if they don’t buy, click, order, whatever... right now, they’re going to lose the opportunity of a lifetime. This isn’t too difficult to do. Here are some options: Offer a time limited prize: “Order now and receive a FREE copy of ‘Build Your Own Bicycle!’”
Offer a quantity-limited prize: “The first 50 people to register will be entered into our FREE prize drawing!”
Create a penalty for not acting immediately: “Every day that you don’t use the amazing ideas in this book, you’re throwing away thousands of dollars! Download your copy and start earning now!” Bear in mind that the kind of action you want people to take will depend on the kind of product you’re selling and the type of person you’re pitching to. If you’re trying to sell cars online for example, “Place your order here” isn’t likely to get many results. People don’t usually like to buy cars so quickly.

You might want to say something like: “Click here for a picture of the interior” or something that's less committal than inviting them to part with lots of cash. Similarly, if your marketing material doesn’t contain all the information necessary for someone to buy, your call to action will only be to invite them to find out more. Below, I’ve put all of these suggestions together in a sample marketing email. I’ve also added my notes to explain how I built it up. Feel free to use this email as template for your own.