You have to remember that even though you're calling on your prospective buyers by email, it's the same as if you were knocking on her front door. Thus it's very important that your material look its best. Everyone knows that the opening encounter with the prospect affects the success of the presentation and whether or not a sale is ultimately closed. Stimulate her interest in whatever you're selling by appealing to one of her basic wants, needs or problems with a solution. Explain the benefits to be derived from ownership of your product or service, and then whenever possible, let her see or read of proof or testimonials from people who have already bought from you.
Testimonials are an extremely powerful tool.
The most important tactic you want to use is creating the fulfillment she'll have as a result of buying from you. Stimulate her imagination, and explain to her how she can use whatever you're selling to her advantage. Finally, and most importantly, make it as simple and as easy as possible for your prospect to buy from you. Don't force her to read a long, drawn out sales agreement or contract. Just make your presentation, explain how purchasing from you will solve her problems or fulfill her dreams.