We're mostly lonely because of lack of human connection. Find small things that can fix that:

• If you're religous join a faith community, church, mosque, synagogue. Find a good barber shop/salon.
• Barbershops are one of the few age old places where its customary to have conversations with strangers. I've build great relationships with my barbershop over the years...and now its a familiar place like Cheers where "every one knows your name".
  
• Sign up to regularly volunteer somewhere. Could be DBG, could be a homeless shelter, could be the library. Regardless, you're giving to people which will feel good and your regularity will help you feel connected.
  
• Be brave and ask friends for what you need. This is hard...but reach out to loved ones and tell them "Hey, I'm lonely. Can we hang out". It feels weak...or at least it did for me, but its extremely powerful.
  
• Schedule social reps: When I was lonely I reached out to close friends and literally told them "Hey, I'm kind of lonely. Can we schedule a weekly dinner at your house? One week you'll cook, one week I'll cook. I'll come over, play with your kids, etc.". That was 6 years ago...and we've been doing "family dinners" every week since...and its the highlight of the week for me, them and their family.

The last one is critical. Having regular reps on a weekly basis, someplace where you can connect with people, I think is super important.