How to get cited and how to boost the impact of one's work?

I can see a few reasons why your paper was not cited as much as you hoped it to be:

• Networking indeed does go a long way towards being cited. In my experience this is especially true for areas where many competing approaches are being published (which, by the sound of it, is true in your case). Even if your paper is published in a good venue, this alone does not guarantee that you will find a critical mass of readers to kickstart the process. Citations are in my experience somewhat viral. Google Scholar, which for better or for worse, is used by many researchers for searching for literature, returns results ordered more or less by citation count. Hence, papers with a few citations on them are much easier to find on Google Scholar than those with 0 citations. Hence, you need to "bootstrap" a bit before citations start coming in more or less by themselves. The best (ethical) way to do this is to network - tell other researchers that might be interested in your paper about it
• You should not per se exclude the possibility that you overestimate the value of your contribution. Maybe the things your approach was good at are not valued as highly by the other researchers. Maybe you underestimate the qualities of some papers that are cited over yours.
• Even if your paper was really good, maybe this was to hard to see at first glance. In an ideal world, every researcher would strive to fully grok each related paper. However, in the real world (especially in busy fields), you have to assume that a reader will at first only casually browse over your paper (and only really read it if it seems very strong to him at first glance). If your paper does not seem strong at first glance, people will not cite it.
• Maybe you are overestimating the value of the venue you published in. In many busy fields, papers published in a "good" venue (as opposed to "the best there is") already have a hard time getting cited. Further, check whether your paper is available with the standard subscriptions that most universities have (e.g., for CS that would be IEEE, Springer, ACM, ... depending on your field of course). There are some non-predatory publishers out there that are simply not available in the subscriptions of many libraries.

The first person who should cite your work is actually YOU. If you simply abandoned your work and you expected others to pick up on it, it mostly does not work this way, unless your work is really ground-breaking. When I search for something on a area I am interested in, it is easy to pick up papers with more citations (which you do not yet have) or authors who are more prolific in this area (which you are now not, since you only published this one paper). Also, people tend to be suspicious when they see "amazing" results, when they are not followed by further work on this area, since that might be some indication that those results were a bit "fishy" to begin with. In this sense, you are the one (at least initially) who should pick up your previous work, improve on it, compare with the newest methods and promote it.

If you asked some years ago, I would not believe in networking either. But the fact is that it works. If you go to some conferences and talk to some of your 'favorite' authors (who are also your main competitors) ask about their published work, talk about your published work (but DO NOT reveal unpublished work), perhaps ask to share methods, do a polite follow-up email soon, you will see that most people respond positively, not because you are sucking up to them but because they see that their work has actual impact. In most of the cases, they also want to improve their methods and see "the polite competition of today as the possible cooperator of tomorrow". So, understand that networking is not just PR but as appreciation to what others and you can offer to the scientific community.

In many fields, the literature moves faster than most people can follow. A journal article can easily be missed. The chance of it being seen now that 5 years have passed is virtually none.

The best way to get your work known in many fields is to get out there and personally evangelize it. Give talks at conferences, talk it up to colleagues, etc. Getting someone else to start using your method is key.