I was a night-time drinker. Like Nic233 I had to completely change my evening routine, including avoiding the couch and TV and having my dinner in the study reading SR.
I started going to the gym or for a run every single evening after work.
I would fix a simple healthy meal after. I made a lot of lists of things I wanted to accomplish - little projects at home, for example.
I kept my place neat as a pin (something I neglected when I drank) and so in the evening there was often some little chore to do that made me feel satisfied and productive.
I usually went to bed early and read a lot of recovery literature or motivational books in bed - in the early days, I found myself falling asleep early.
As for going out to places in the evening where you'd normally drink, it would be a good idea to take a break from those events for a while till you build your sober muscles.
Early sobriety is a great time to take stock of yourself, learn about yourself, reflect on why you're an alcoholic and make plans for the next few months of recovery, on which you can build your sober life. It's important work.
There will always be an opportunity to "have fun" but in my experience it was better to focus first on my sobriety and then open up to the world of socialising gradually as I learned about the new sober me.