Much of marketing involves testing which is a fancy word for trial and error. My dad was a top Madison Avenue copywriter back in the day - one of the original Mad Men - with a roster that was a who's who of Fortune 500 companies.
When he would submit copy to a client it would always be tested on a very small slice of the client's database. If the test produced the desired percentage of response then it would be used for the entire database. If not then back to the drawing board.
You can increase your chance of success by getting surveys done first which you can then base your promotion on. My dad wrote his copy instinctively without surveys. But surveys cost money and most dentists, especially if they're struggling with new patients, have a fairly limited marketing budget.
So what to do?
It is vital that you keep track of each marketing action you do and the results from those marketing actions. You can try different marketing actions to see what produces response with the best ROI. What will work in one town may not work in another town. Door hangers might work great for you. In another town they may not. They may even be a turnoff. Who knows until you do some testing?
Equally as important as to whether you use door hangers, newspaper ads or even Google ads is what the offer will be. For example a discounted new patient exam might produce a response in your area or it might not. Perhaps an offer of teeth whitening will produce the desired response. It's all about testing (trial and error) to see what works for the best ROI.
Personally I like LOW cost marketing which, IMHO, eliminates any kind of mailings. Don't get me wrong, mailings done correctly, can give you results but they are very costly and if they don't work you are out of a lot of money. I spent thousands and thousands of dollars on mailings each week before the Internet age. I think we did our last mailing over 10 years ago.
With our clients we like to approach marketing as follows:
1. Institute a good internal marketing program the success of which is based on assigning responsibility of it to one staff member and monitoring the program with weekly statistics. For an established practice we generally find that's all we need to do to generate the number of new patients needed for the practice.
2. If internal marketing alone does not produce the desired results we recommend looking first at the least expensive overall marketing actions available such as newspaper ads where financially feasible (rural and suburban towns), websites with SEO work as well as Google PPC campaigns provided you hire somebody who really knows what they're doing. Websites, done correctly (see Mike Barr's book) can be a bit costly but the costs are up front for the most part so once the website is up you're really only talking the cost of the hosting fee on a monthly basis. One might also consider Val-Paks and improving signage at the dental practice location. In fact, good office signage would probably be the first thing to do as far as external marketing If all else fails then mailings might be an option but again you're talking big bucks which may produce a good ROI or not.