There are all sorts of methods and practices for maintaining your network and increasing connections but here is the one I have found to be the most effective and requires the least amount of effort:
Make Your Connector Happy
Think about some opportunity that has come your way, a new job, an interview, or even a friendship. We tend to focus on the end result and the provider of the result but if you think about what the genesis of that connection was, you might discover some interesting things. For instance, the other day I had an interview with the Unmistakable Creative podcast. It was an awesome interview and I had a lot of fun. I of course thanked the host for the opportunity and most people would do the same, they would also stop there. However, I like to think about how that interview came about and it was because of a friend of mine who I only speak to every couple of months and he made the suggestion. This was over a month ago, he offered, I said yes, and he introduced me to the host.
To me, going back to the person that made that original connection and thanking him for making it happen is actually more important. That person is a "connector" and while there was a ton of value to the relationship made with the host of the podcast, the "connector" has been a part of my life longer and because he isn't providing the end product is able to present me, in my best light, to people that he knows and who he thinks would mutually benefit from the relationship. So I'm simply letting my friend know how much he is appreciated and helping him to keep me in mind for other things.
I have a simple system for making all of this happen. I try to note down any introductions I make or get in my nightly iDoneThis.com journal entry. To make things simpler I write "X introduced me to Y". Then whenever I have some event happen like an interview or a business opportunity, I simply search my Gmail for "introduced me to Y" and get right back to that entry so I known who I need to thank.
It's a move that tends to be unexpected, and greatly appreciated. Now that's next level networking, Less Doing style.