After the appropriate celebratory period, it depends where you are in your professional life.
If you are student then probably you are asking your advisor what next? Probably you were "rabbiting away" on the paper pretty single-mindedly. Maybe this completes your research quota for your degree and it's time to write the thesis. Or maybe you will do the next version of the research with "go-faster stripes."
If you're a post-doc or junior prof, look around for something new and exciting. Not necessarily immediately following on to the current work, but probably related. You are building a base.
If you are tenured prof, what's next in the research queue? And if no queue, get busy making a queue. You should have a program of ideas and possible research topics and tasks. If you are a senior type, you might even have several queues with more or less connection between them. If you are in a place where you have students, go walk around and ask each of them how they are doing and if they need some kind of push to keep them making progress. It's a time for a deep breath or two before getting back into hard work mode.
Maybe you have time and attention to look to your personal life with more than usual concentration for a week or two. Maybe that special somebody would be glad to have your full attention for a bit. Vacation? Even a small one to something local?
Ask yourself if this is the time to do "that" research. You know, the juicy one you've had in your back pocket for years. The one you have not told anybody about. Do you have time and stability to get into some new big thing with some speculation and risk connected to it?
Read through the "gossipy" journals in your research area and see if there's any "new big thing" you would be curious to expand into. The kind of journal that has "Today" in the title.
Anything you want to apply to or for while your head is out of research space? Grants, conferences, funding for a research fellow, funding for new equipment, funding for etc. I find filling in those forms spoils my mood for concentrating on the interesting stuff. Get it done now if you can, while it won't be distracting you from doing research.