Just as, when we are communicating through speech, the tone of our voice can add much to the meaning of our words, a good writer can convey tone though the written word. This can be done in a myriad of ways, and it wouldn't be bold to venture that you yourself have made a conscious effort to employ a certain tone on more than one occasion, whether through a text message or on an internet message board - it may be that you employed an ALL CAPS approach to a PARTICULAR SITUATION, or you might have made use of an eggregious number of exclaimation points(!!!1) The point [ha!] is that every voice employs tone to some degree or other, and as with any art, whereby it is applied with a more delicate hand, thereby is a greater measure achieved. Or, something like that, anyway.
Read this transcript of the 2005 commencement speech to the graduating class at Kenyon College, delivered by David Foster Wallace. Commencement speeches quite often make for excellent studies, as the formal requirements of the occasion necessitate a particular tone on the part of the speaker. Add to this the speaker's desire to not bore their audience by sounding overly didactic, and the result is a masterclass in the use of tone, especially from such a clever writer.
In this letter to a friend the young Hunter S. Thompson gives his best response to a request for advice. Even at the young age of 22, the author's patented and very readable style is immediately noticable. Pay close attention to the techniques he uses to convey tone, and the way in which he uses that tone to mediate between the instructional nature of his message and the obvious desire to not appear arrogant before his intimate.