How do you stay focused if your co-workers are continually interrupting your work?

Honestly, that rarely happens. If I do feel like a coworker's actions are distracting me, I would make it known in a polite way and remind them of their responsibility. Always create an environment where dialogue with your co-workers is possible.

I normally listen to what they have to say if it's a co-worker that doesn't sit in my room. If they only want to chat I either go with it because I need a break, otherwise I tell them I got a lot to do but will come by their room when I'm finished.

Me and my co-worker that sits together with me do often chat. However, when we need to do work or when we feel like we've been talking and interrupting each other too much we say that now is work time and set a limited amount of time to just do work before going back to chatting. And so on.

If I have to perform work that requires me to be focused, I put on noise reduction headphones and listen to playlists available at youtube that let me be focused. There are a lot of youtube channels that provide those playlists, it is a matter of finding your "white noise" preference. There are also a lot of white noise apps that I have tried, others with nature sounds, others with binaural frequencies. It is a matter of finding the right ambience for you to focus. Practicing mindfulness regularly also helps to focus on your work and not be distracted by the people walking and talking around. Also practice leads to perfection!