Persuasive letter writing can employ similar techniques as in any other form of writing (be it report writing, essay writing etc.). One of the techniques could be to ensure that specific vocabulary is used to get your point across. This means that instead of either beating around the bush or using vague/ambiguous vocabulary, one should give the information that's required in a coherent and precise way, so the reader doesn’t get confused. The skill to use the specific vocabulary should be developed over time through learning better words in the first place and then cleverly applying them in suitable situations. Another technique could be to structure the letter in the best way possible. If the person is giving the best arguments but they are not structured well, there’d be a high probability that the reader would either forget about them or not be persuaded by them. The text needs to be structured in a manner in which different arguments, reasons etc. are arranged in a prominent manner. Further, the writer could apply rhetorical questioning to ensure that the reader re-thinks about his/her existing beliefs. The point of the writer would also be put forward in a non-passive way and he/she would be saved from producing uninteresting and never-ending descriptions. For instance, instead of mentioning ‘this technique would help the person in achieving success and everybody would like that’ one can simply say ‘We’ve seen the tools lead to personal success and who wouldn’t like it?’ This type of rhetorical questioning would target the person reading the text very directly and would have a higher chance of being persuasive There can be quite a few other techniques as well but following these ones first would make a considerable difference in the writing skills!