The fifth finger is the smallest and weakest, and requires special exercise to develop strength equal to the others. Playing the piano requires evenness and balance between all four fingers and the thumb. The problem here is, if you look at your hand, each digit has its own needs. Your fingers are all different lengths. Your thumb plays at a different angle. Your fourth and fifth fingers share tendons and so are generally the weakest and least independent.
So, how do we strengthen the fifth finger and gain independence in it? Scales are a necessary tool, of course, but they are actually not very helpful for the poor pinky. In most scales your fifth finger will only play twice in your Left Hand, once in your Right Hand (and sometimes not at all!), so it's not getting the same workout as the other three fingers. Czerny's School of Velocity studies are better for developing strength and agility as he often uses repeated motifs for this purpose. Hanon is another example, however he is quite a divisive figure in the piano-teaching world because, if not taught correctly, his exercises can actually cause damage to students' fingers. (Not to mention they are quite boring and mechanical and only use white keys so develop no sense of tonality other than C Major). I only use his exercises sparingly; in fact there are only two Hanon Exercises I use with students (No 1 and No 6) as these exercises do focus on the fifth finger lift.
Another activity is the Leschetizky Solution. Done gently and correctly, this can be a useful activity to help develop finger strength, especially in fingers 4 and 5. This activity requires the student to depress all five fingers at once and then one by one, lift and press each finger into its key four or five times. You can watch a good example of this here . My only thoughts on this video is that it might help to practise this exercise one hand at a time first so you can really focus on what each finger is doing individually before going hands together. A good aspect about the Leschetizky Solution is that you can do it away from the piano which also helps to reduce the instinct in beginner students to 'push' at the keys and instead work on freeing up the tendons in the 'lift'.
One of the most important things to be aware of when doing technical exercises is tension. Sometimes the fifth finger sticks out or plays stiff because it is tense. Melanie Spanswick writes a good article about tension in the fifth finger and what to do about it here
Remember that developing technique can take years, so always go gently at first. If you ever feel pain or strain at any point, stop what you are doing and discuss with a teacher. I'm quite passionate about developing technique because as a student, none of my teachers ever corrected my playing technique until I reached university (Whiplash, anyone?). Building technique takes a lot of time and a lot of practise, so don't rush, just focus on little gains.
As always, Happy Playing!