Try not to make your paragraphs longer than 3 or 4 lines. When your paragraphs are short, people will read them easily. But if they are long, it will seem overwhelming to people. The colors you use in your newsletter design is important as well. So you should know a little about colors psychology. It's not hard. You must already know about the effect of every color on people, before designing or choosing your newsletter template.
Templates save you money: If you use a royalty_free template, it likely costs less than hiring someone to create a custom graphics package for you. You could easily spend hundreds (or possibly thousands) of pounds on a custom motion graphics opening, for example, whereas you can frequently purchase a royalty_free template for under £200. Of course, the royalty_free template isn't as unique as a totally custom template, but it definitely costs less, and you could always customize the royalty_free template to make it more unique for you.