In addition to the great comments mentioned, Over the years I've found a combination of approaches that work well for my photography business.  I've settled on two primary networking associations where the types of businesses I want to work with are represented. One group includes: Governments agencies of all types, Construction Companies of various sizes, and a variety of business representing many other sectors.This association meeting attracts about 120 guest to each meeting. The second Association focuses on Tourism within the state which has also lead to photo projects for National Associations across a variety of sectors.  There are opportunities to sponsor a networking event which entitles you give a short presentation on your business. I've had this opportunity at least twice per year the past couple of years. When I photograph an event, I'll make sure to get photos of the individuals I want to connect with. I'll take their card and email the photo with a note. Basically, there is no one way. It depends on your business type and the types customers you want to work with. I talk to people everywhere I go. I have business cards with me at all times. I'm posting to my website and social media, driving traffic. Linking to other sites.  

Basically, using all the methods available to communicate to a prospect. Oh, yes, and all of this work takes lots and lots and lots of time. Every connection is like a seed being planted. They grow at their on pace. There are no short cuts for doing all the tedious work.