Free HTML email templates are a boon to most small business or campaigns that are restricted in scope. This is because there is nothing better than having a free option for a non-billable exercise. Most company newsletters, event invitations, newsletters, tend to use some kind of a template or the other. There are the obvious benefits to using free options but you must remember that as your business operations start to scale up and the need for communication increases, the robustness and the needs from your templates will increase to a point where you will not have an option but to get your own design team or go in for a paid service.
While you are still indulging in the free option, there are some design guidelines that you must bear in mind:
Color: Color is a very contentious issue and there are many schools of thought as far as what kinds of colors will make for an appealing email and what will not. However, one simple guideline that you can bear in mind is that you should always try to reflect your corporate colors in your emails. If you are a business entity, this is a simple act of repurposing the templates that you used when you were making your website. Apart from this, ensure that the HTML HTML templates that you are going to use do not have loud or senseless colors as spam filters sometimes parse HTML codes for odd color combinations.
User perspective: What really appeals to a user is more or less a matter of conjecture or a matter or guesswork. However, there is one aspect about the user that you must anticipate. This is the aspect of the user's email client. Most email clients today block out the display and preview of mail content that contains HTML or imagery. This can really be a spanner in the works undoing all the good work that you have done. Therefore, as a tip, ensure that your templates are not purely dependent on HTML and heavy imagery.
Technology: This might be an aspect that is not available to most free email templates but is worth looking for. In a Web 2.0 world there is not bigger credibility you need to establish yourself as a serious player than the use of video. Therefore, look around the net for free HTML email templates that also give you some freedom to embed video or audio. This may be wishful thinking but you can also go around this problem by have access to coding expertise.
These are some of the basic guidelines to follow but they should be applied judiciously and you must remember that the content you are sending has a great effect on design as well. Therefore, you should also have a range of designs at your disposal to use. A problem might crop up here if you end up choosing the free option; therefore, evaluate your options carefully.