The 4th Finger…
For a pianist, the fourth finger can be very troublesome, linked by a tendon to the 5th, it doesn’t have the lifting capability of finger 3 or finger 5. For anyone who is new to this, try placing all 5 fingers in a curved manner on a table and just try lifting finger 4 (the ring finger). See what I mean – not so easy!
When learning to play 3rds or a 3-note chord C-E-G for example, many beginners find this position very difficult.
Try this method from C.C. Chaung, The Fundamentals of Piano Practise:
The finger independence and lifting (see below) exercises are performed by first pressing all five fingers down, e.g., from C to G using the RH. Then play each finger three to five times: CCCCDDDDEEEEFFFFGGGG. While one finger is playing, the others must be kept down. Do not press down firmly as this is a form of stress, and will cause fatigue very quickly. Also, you don’t want to grow any more slow muscles than is necessary. All the depressed keys must be completely down, but the fingers are resting on them with only enough downward force to keep the keys down. The gravitational weight of the hand should be enough. Beginners may find this exercise difficult in the beginning because the non- playing fingers tend to collapse from their optimum positions or lift involuntarily, especially if they begin to tire. If they tend to collapse, try a few times and then switch hands or quit; do not keep practicing in the collapsed position. Then try again after a rest. One variation of this exercise is to spread out the notes over an octave. This type of exercise was already in use during F. Liszt’s time (Moscheles). They should be done using the curled as well as all the flat finger positions.
For the finger independence exercise, try to increase the speed. Note the similarity to PS exercise #1, b. Parallel Set Exercises for Intrinsic Technical Development. For general technique development, exercise #1 is superior to this one. The main objective of exercise #1 was speed; the emphasis here is different – it is for finger independence. Some piano teachers recommend doing this exercise once during every practice session, once you can play it satisfactorily. Until you can play it satisfactorily, you may want to practice it several times at every practice session. Practicing it many times at once and then neglecting it in subsequent sessions will not work.