Proper wrist and shoulder alignment begins with the placement of your hands. With your hands grounded palm down, pretend you have a line that comes out between your index and middle finger. This line should match the outside of your shoulders for proper placement in most poses. From here, spread out every finger and press your finger pads into the mat, then the mound of your index finger, followed by the mound of your thumb, and the rest of your palm. This will allow only the middle indentation of your palm to come off the mat.
For help grounding through the mound of your index finger, inner rotate your forearms allowing the inside lines of your elbows to face each other. Flex your biceps to keep from hyper extending your elbows and bring the top of your shoulders up and back as your shoulder blades move closer to your spine. For a better range of motion and to protect your shoulders plug your shoulders in towards your mid-line (the center of your body). This motion is similar to plugging something into the wall. To really understand the feeling of plugging in your arm bones, bring your arms out in front of you and reach away from your body, this brings the shoulders off the back. Now bring your shoulders on the back by bringing them closer to each other. When moving through a series of poses, try to hold this hand position and engagement of the shoulders, it will protect your wrists and shoulders from injury.
It is a common misalignment to lift the mound of the index finger off of the mat. When this happens the weight the hands are supporting, rests fully on the outside of the palms and wrists. This can cause serious damage to the wrists and shoulders. Ground through all four corners of your hand especially when moving through a series of poses (such as a vinyasa) and your body will thank you.