In college, you always had something to focus on that would distract you from your life at home. You'd go for days, even weeks, without communicating with your friends and family, subsisting on what you could glean from social media. Then they'd call you on some Sunday, and you'd talk for an hour or two, and after, you'd think "Man, I should really talk to them more," before going back to writing another 2,000-word paper (read as: playing Final Fantasy X for the fifth time). But now you're out! There's nothing stopping you from having a happy and healthy relationship with the people what made you alive in the first place, and here's some small bits of advice on how.
If you live with them, help them around the house and behave pleasantly. Otherwise, do you. Living with your parents can be tough, especially after you've had that initial taste of sweet dorm-life freedom. But you may as well make the best of your situation and try to be nice and patient with your housemates.
If you live within walking distance, help them out when they ask you to and go over to see them on Sunday, or any equivalent day where you all have the day off. It doesn't have to be for too long, just a couple of hours so that you can fill them in on what's new in your life and find out the same from them. This can be supplemented by stopping by after work every day for a little bit, and maybe some tidying up after them in regards to dishes and kitchen table clutter.
If you live across town, try to go and see them every week or two, again on Sunday, and help them out if you can and have the time to drive a half hour or less. Otherwise, try to help them over the phone.
If you live out of town/state/country, call them every three days or some other agreed-upon interval, and try to visit them whenever you're in town. Write letters for special occasions or send them a souvenir of where you live or some flowers if you can afford it.
"But Tristan," you say, "This all seems a little overly formulaic and a little cold when it comes to the people who raised you." To which I respond: yes, but if I didn't follow this system, I still would never talk to them unless prompted, and that is just not fair to them. Life outside of college can be just as busy and distracting as life inside of college, and as has been said previously, keeping in touch with people can be hard.
This is not meant to be a response to a guilt trip or to be something expected as a payment for services rendered, but more as something you just do because it's good for both parties involved and it's polite. It's polite to keep in touch with people who love you, and who you (presumably) love back. I do concede that there are situations in which this is probably the worst thing you can do for yourself. Some parent/child relationships are just too toxic. But in that case, find a person you do regard as a parental figure, and apply the same rules for them. For someone to spend as much time thinking about someone else as a parent does for their child and to hear nothing back for long periods of time can be torturous. So ease some of that tension and pick up the phone.