It's important to celebrate. (I think that's just as true in life as it is with habits.)
When it comes to sticking to better habits, there is an important reason to always reward yourself: we want to continue doing things that make us feel good.
And that is why it's especially important that you reward yourself each time you practice your new habit.
For example, if I'm working towards a new fitness goal, then I'll often tell myself at the end of a workout, "That was good day." Or, "Good job. You made progress today."
If you feel like it, you could even tell yourself "Victory!" or "Success!" each time you do your new habit.
I haven't done this myself, but some people swear by it.
Now that we've covered the science of habit formation, let's talk about how to use it in real life.