I personally play some very easy beginner etudes sometimes and try to make it sound as good as possible. If I don't do it for a long time, it can be surprisingly difficult but it gets better very quickly. Once I have done that, my whole playing feels better. I also play all my scales every day and spend time to play a few long tones when I warm up to maintain fluidity and a good tone.
Of course you can't spend your whole practicing time doing this. You have a lot of music to prepare after all but do take time to water your roots and you'll find it easier to grow your tree.