You should choose a neighborhood or two and send the people living there a postcard every 30 days. Find a direct mailing list mail company that can set up mailings on a schedule and let them do the work for you. Keep in mind that it is more cost effective to print a larger quantity of mailers at once instead of printing a smaller batch every month.
The design of the mailer can also be consistent. Don't worry about coming up with something new every time mailing list either. You might be tempted to have a different design each for mailing and list a home you recently sold. People have short term memories. They are not going to remember what property you sold last month. The thing they will remember is you.
Include your photo and a short bio and personalize the design. If you are a local and live in the area boast about it. The fact that you know the neighborhoods is a bonus. Try to come up with a catchy mailing list slogan something people will remember. Don't be shy; the purpose is to make an impression that will last. When it is time to sell people are always in a hurry.