My husband and I both have several families on our routes that don't allow visits (and/or just don't ever return calls or answer the door). I send my visiting teaching sisters (who don't want visits) a simple little newsletter that I make up every month with a message, upcoming activities, etc. I feel like a photocopy of the lesson from the Ensign isn't enough. I want them to feel included and know that I genuinely care.
Trying to be helpful, I offered to print out the monthly First Presidency lesson and mail it to the people on my husband's route who don't have visits. I didn't have any way to know whether or not the recipients would read them or throw them in the trash, but I started thinking- what if they do read them? What else would we say to them if we could? What might I include that could spark interest, so that they might actually read subsequent letters? So, patterning after my visiting teaching newsletter, I started making a home teaching newsletter. John and I discuss what to put in it (always including an appropriate portion of the home teaching message as part of the newsletter, instead of just printing off the whole thing) and I do the leg-work.
My number one rule is to always be positive. I try not to include anything unnecessarily condemning-sounding (no out-right calls to repentance, or anything like that). I try to be sensitive, thinking about how a long-time less-active/inactive member or a non-member spouse might react to what I have sent. I don't want to water-down doctrine, but at the same time, outright offending someone by mail isn't going to benefit anyone. I also try to include things that might be interesting to the particular person/family. Since there are different family/individual circumstances and ages in the different families that we serve, there are sometimes several different versions of the newsletter every month. For example, for an older couple I might include information about genealogy, but for a young family I might include information about an upcoming Primary activity.
This month's newsletter included a portion of the First Presidency message from the Ensign, a summary of an article (found on providentliving.org) about improving family finances, list of upcoming ward/stake activities, information about church (meeting times, location, etc), and information about using the family history library (hours, location, general info, mentioned that its free, etc) and using online resources for family history. I try to have a balance of spiritual message and other items that might be helpful to any person/family.
There is also always a note at the end from my husband, which always says something to the effect that he is their home teacher (in case they're wondering why they're getting this newsletter all of a sudden) and that he looks forward to getting to know them, etc. and also includes his phone number.