I started doing some of the following a little bit during 2017, I want to standardize these for 2018.
At the end of a project, I have stuck my card on to something, the rack, a tech panel, somewhere and I show it to the client so they know they have my info stored near the gear. I then talk about about the system or am asking how they like everything and that is when I mention referrals and hand them a couple of business cards. They now have extra business cards (only 1 or 2) to hand out to someone they know. Depending on the client and the relationship I would also mention on line reviews and how helpful they can be for my business. Again depending on the relationship I will either go on line for them and see if we cannot do something right there and then, or let them know I will be sending a link they can click on and fill out whatever nice things they might want to say about me and the work I have done for them. I also plan on sending out emails every 4 or 6 months with something new I am working with (Voice control etc) or upgrade info / ideas for those that have older systems. I have to figure out more about how to best use Facebook and other online things. Youtube videos showing new electronics or other things might also be explored.