Tadasana, or mountain pose, is often considered a beginner pose. However, this pose is important to work on, and revisit in great detail occasionally, regardless of your experience level.
Why? you ask. Aren't we just standing in one place, breathing?
While it may look that way, there is quite a bit going on in this pose, involving your entire body. And by practicing it regularly with a beginner's mind, you will be better prepared for alignment in every standing posture your practice may present.
Begin with your feet parallel, either together or slightly apart (no further than hip distance). Press firmly and evenly into the base of the big and little toes and the heel. Firm the legs, draw the navel inward and notice the downward movement of the tailbone. Lengthen the spine, stacking the shoulders over the hips and extending out through the crown of the head. Draw the shoulder blades onto the back of the body, and allow your arms to release down by the hips. Gaze is forward and chin is parallel to the floor. Take 5-8 breaths.
Notice the subtle movements in your body. Balance. Breathe. Center.
(This pose may also be modified by sitting on the edge of a firm and stable chair, feet pressing evenly into the floor, arms by your sides or resting on the thighs.)
Contraindications: Insomnia, low blood pressure, headaches.
Enjoy your breath, enjoy your practice.