If you fall into something, it happens by chance. It is not something you do on purpose. So, perhaps, by luck you may fall into a good habit; you might fall into the habit of studying after dinner (because there was nothing else to do).
However, your sentence sounds like advice to do something on purpose. I don't think fall into works in your sentence. For your sentence, I would say something like "It is important that we get into the habit of studying regularly" or"acquire the habit of studying regularly."
You fall into bad habits, because it is easy to develop a bad habit without intending to. Usually our bad habits are things that we do often because they are easy or pleasant in some way, until they become habits and difficult to resist. Thus we 'fall into' a bad habit out of laziness, or self-indulgence.
The actions aren't by chance, but the 'habit' is. You don't set out to acquire a bad habit. It is simply the by-product of repeated individual choices.
That is my view, at any rate, which is why I expressed the idea as I did.
Added: In contrast you might deliberately decide to develop the good habit of brushing your teeth every night. You begin to brush your teeth regularly, with the hope that over time it will become a habit, something you do every night without thinking about it.