If serenity is about accepting what you can't change and acting on what you can, then this blog has spent a lot of time discussing how to let go and less about how to act when acting is called for.
Here's my suggestion of the day:
Make a list of all the hard things that make you seize up when you think of doing them--and then just try one step towards one today.
Such a list has the potential to cause more suffering than it alleviates--at least at first. Getting clear about what is stopping you, and looking at each big scary thing in its face, can feel torturous. It can look like a mountain or the Grand Canyon, depending on your sensibility. Either way, it seems like something you can't conquer.
The good think is you don't have to conquer everything at once.
If you have a business plan you may have your list of what Franklin Covey calls "big rocks" already written down: Make $X this year, break into certain publications, etc. That's a great thing. That plan should also give you steps to make those things happen: If you want to increase your income significantly, what mix of clients/projects will bring you to that income level? How much work is required?
Take one of those big things and break off a small piece to start on. Today. Don't hold back. Don't block out the business plan because it seems more like a pipe dream.
Just start, with the faith that something will shift, even if you don't get the results you want in the timeline you've determined.
If you don't have a business plan, chances are your list of scary Big Rocks may seem like a wish list instead of an action plan. So maybe your first big hard thing on the list is to finish or start your business plan. It's not too late. Gather a friend in your field and meet once a week for an hour until you get it all down. It doesn't matter if it doesn't get done till June. That just means the second half of the year will be that much more serene and prosperous for you.
The key here is to remember that mountain doesn't have to scaled today. Just make a start on it, some small bit. And then show up for it--and your business--again tomorrow.