There are quite a few sources that help you out with tips on building a marketing letter. However, the following lines have the best tips available to write an effective marketing letter.
The things that you write should be brought about in such a way that it meets the requirements of the person you are addressing to.
The language used should be basic, nothing very fancy. If complicated then the impression would not be good.
You must look into the benefits of the letter. The things that you are paying focus on. Those things that may earn you benefits. Make sure they are presented well, so that it hits the right chord with the person who is reading it.
Last but not the least, utilise the power of the magic word YOU. If you refer the person as YOU, then you are making this more as a personal conversation and personal reference.
With these tips you can go in to write a real nice marketing letter.