1. Are focused on one main purpose
The first thing you need to do, is to think about what you want the person to do (do you want them to call you, to buy a product, to start trusting you, to sign up to an email newsletter etc...) and the best way that you can get them to do this. Think both from the other person's perspective and what would make you respond or buy something if you were in their position.
It is not wrong for the email to have a secondary purpose (e.g. sign up to an email newsletter, become a follower of your company on Facebook etc...). But if you include one, make sure it doesn't detract from the main thing that you want your follow-up email to achieve.
Once you have decided on the main purpose, focus the email on it.
2. Contain a good reason for sending
Although the main reason for sending sales follow-up emails is to sell (or to eventually lead to a sale), they shouldn't appear to be about this at all (because they are not very successful).
The email should contain another valid reason (although false reason is probably a better name for it) for why you are sending the email to the person (e.g. giving them free information, an invitation, ask them to confirm something, ask if they need anything etc...).
You should use this valid/false reason as the subject of the email (e.g. 'buyers guide to cameras', 'your recent download', 'questions about...' etc...).
You can then write in the email (like a second thought) about what the actual/real purpose you're sending it for (e.g. to get them to speak to you, to tell them about a new product or offer etc...).
3. Don't have to try to sell
Although if done correctly, there is no problem in writing about your company's product(s)/service(s) in a sales follow-up email (see above for how to do it), you can also write the email without saying anything about them.
In fact, some very good sales follow-up emails don't even mention anything about the product(s)/service(s) that they want the customer/person receiving it to buy. They use the follow-up email as a way to build up a relationship/engage in a conversation with the customer/person (by getting them to respond or become a follower of a Facebook page etc...) and/or find out more information about them and their needs.
Using this type of sales follow-up email, you'll both have more opportunities to sell in the future and it'll be easier because they know you and you know more about them.
4. Make the person receiving the email respond
The best way to sell things to people is to get into a conversation with them. It gives you more opportunities to try to persuade them to buy your product/service. So, find ways to make them respond to the email you have sent them.
Asking them questions in the email is a good way to do this. For example, 'I'd just like to confirm that you've received it and found it useful?' or 'How are things going with the redevelopment?'. When people are asked questions like these in emails, many of them will feel obliged to reply.
You could also offer to send them some free information/guides. I would recommend that you include a taster in the email (e.g. the first couple of pages of a help guide) and tell them if they want to receive more then they'll have to contact you by email or phone.
Another way to get a response if you have the customer's/person's phone number, is to tell them that you'll call them if you don't receive a reply from them. But be warned, this is can be seen as pushy/aggressive. And although it can annoy people, it does work.
5. Explain the previous contact
To make sure the person reading it doesn't think the email is spam, explain when and what the previous contact you had with the person was at the start of the email (e.g. 'we spoke yesterday about' etc...). Do the same if the email is a follow-up to some action a person has done on your website like downloading information or becoming a member (e.g. 'you recently joined...' etc...).
6. Are short
The shorter your email, the more likely that people will read it. Also, don't use long paragraphs.
7. Are personalised
Use both their name and your (or somebody's) name in the email and include things that have happened in the past (e.g. receiving information, having a meeting etc...). People are more likely to respond if they have the name of a person than just the name of the department or company.
8. Use a person's email address
If you have had actual direct contact with the person and they know your name, you should always use your work email address to contact the person.
If you haven't had this contact before and the email is a follow-up to some action a person has done on your website (like downloading something) or through the company, the first email should come from a general company email account (so the company's name is displayed as the sender). But you should include a contact name somewhere in the content.
9. Use a less formal style
For most follow-up emails you don't need to use a very formal style of writing. Use a writing style and vocabulary you would when writing an email to a work colleague/co-worker (use 'Hi Peter,' or 'Good Afternoon Peter,' instead of 'Dear Mr Smith,').
10. Use certain phrases
There are certain effective phrases which can be re-used in most types of sales follow-up emails (e.g. 'by the way', 'have you heard' etc...). To learn more phrases which you use in your own emails, see our exercise on Sales Follow-Up Emails.
11. Use text in the email
I think that using lots of images (of the products) in a sales follow-up email makes it look like an advertisement. I prefer to use just text in follow-up emails, it makes them seem like more of a genuine email, not something sent out on a mailing list.
If done correctly, sales follow-up emails can help you make both more sales now and in the future. In my opinion, being too direct and trying to sell in the email is not the best way to do it (especially if you haven't had any contact with the person before). It is easier to sell to people who know you than to people who don't.
How you write it (e.g. the style and email length) and what you write (e.g, the reason you give for sending it) are very important in getting the customer/person to respond how you would like them to.
Once you have learnt what a good sales follow-up email should contain, it just requires practice and time to master. Make different versions of the email (with different vocabulary, false reasons for sending or where you do or don't talk about the product/service you want to sell etc...) and see which version converts/works best. That's it.