That the weird thing. I don't (market myself). I made website but I don't get leads from it. It's just a portfolio. I am very friendly and I do keep up with people I worked with decades ago but that is the extent of my "networking".
I know some people can go 30 years and not have any friends they used to work with. At the very least, you should make contact on LinkedIn for your (former) colleagues when you leave a job. Drop them a line once in a while. “Ping” them a text at Christmas, etc. You don’t want to wait until you need work to start building your network.