Word of mouth is VERY BIG. I was fortunate to have worked with some people that always know how to reach me. Those people know I don't mind people calling or emailing, so they share my contact information. In my business, drop ins are not okay. Scheduling is important. You have to return calls and emails at some time of the day, so make time for it, and reach out to people you haven't heard from in a while. They will appreciate that you were thinking of them. 

Reaching out on birthdays and anniversaries are great on social media, but a personalized card will be placed in a place of honor in a customer's home or business. Honestly, I do generic cards and write birthday, anniversary, new location and new service information into the message. New clients find me when I do a combination of social media, greeting cards, and issue cards when I meet new people, because I ask people to refer others to me.