When you’re developing a new habit, if you catch yourself following your old habit, go back and do it the new way.
For example, let’s say someone tells me about a new driving route that’s faster than my current route. No doubt I’ll find myself slipping into the familiar route. When this happens and I notice, I can turn the car around and take the new road. This helps solidify the new road as the road I want to take.
Of course, if course correction is costly don’t do it. But if it’s a few minute detour, no big deal. Force yourself to go back and do it the “right” way or the “new” way. This will markedly decrease the time to form your new habit.