The placement of your body in relation to the keyboard and to your hands on the keys can determine how comfortable you are while playing and how quickly you can press the keys when necessary. A "hunched over" feeling when sitting at the piano and tight tops of your hands are both signs of poor posture.
Use an adjustable piano bench rather than a chair or stationary bench. People of different heights may need to put the bench in different positions to be comfortable while at the piano. A good rule of thumb is to keep the height of the piano keyboard at your belly button. Sit about elbow length away from the keyboard and keep your elbows off of your knees while playing.
When placing your hands on the keyboard, avoid letting your wrists drop to rest on the base of the piano. By dropping your wrists, you lose a great deal of flexibility and speed as well as create undue tension in the tops of the hands just behind the fingers. Your fingers should be curved downward and at a natural slope.
Imagine that each of your fingers has a number from one to five. Your thumb is number one while your pinky is number five. When practicing technique, separate melodic lines into smaller sections. Always try to keep your thumb (number one) on the lowest note in the section. Roll your thumb after your third finger when playing scale patterns. For example, a full upward scale fingering pattern would be one, two, three, one, two, three, four and five. The same pattern descending would be slightly different at five, four, three, two, one, three, two and one.
Pinky technique is important when playing the piano. You may need to press an isolated key 20 keys above your current playing position. A good method of practicing this is by starting in the middle of the keyboard and playing a five note scale on middle C. After playing the scale, quickly move your hand up two octaves to press the C. You may also choose to use your index finger to strike the higher C, but doing so will not develop pinky technique.
Reading the music should be your prime consideration when playing the piano. In other words, your practice sessions should focus on eliminating the need for you to look at the keyboard. Choose method books that allow you to become familiar with small sections of the keyboard and relate those to every other portion. Never move on to more complicated music until you can play previously learned music without watching your hands. Doing this will develop music reading and keyboard technique rapidly.