Tadasana, Samasthiti , or mountain pose, is a great way to start off any practice; even if you are not practicing Surya Namaskara. Samasthiti helps to bring awareness to the proper posture that should be held in all yoga poses; it is a good point to start for beginners, and a great refresher for advanced students. Standing in Samasthiti brings awareness to the grounding and uplifting nature of yoga, it is a neutral pose to begin awareness to the bandhas, and it also begins the process of opening the heart center with the positioning of the shoulders.
How to Practice
Stand at the top of your mat wit your feet hip distance apart or with the big toes touching. You may have your hands at your heart, or resting at your sides engaged, with palms facing front. Lift up your toes from the matt. Slightly tip this way and that on your feet, feel how you are caught from the balls of your feet, and your heels. As you release your toes feel a sense of grounding, and as you ground feel the energy move up your spine creating a lightness in the body.
As you slightly engage your calfs and thighs, feel the energetic lift in the arches in your feet. Inwardly rotate your thighs. Engage the low belly, tucking the tail bone slightly under with a scooping effect (this can also be thought of pushing your pelvic floor down, or a Kegel exercise).
If your hands are at heart center, release them down to your hips, engaged with palms facing forward. Inhale your shoulders up towards the ears. As you exhale to release them down pull them back so that they melt down the back of the rib cage. Have your gaze forward.
Tadasana or Samasthiti can be a great place to set an intention for yourself during practice, as well as an intention for something outside yourself. It is important to remember all the different checks you go through during this pose, as each one can be checked in every other pose in your sequence. Particularly the low belly being firm during practice is important to protect the lower back.
Standing in Samasthiti throughout your day can also help improve your posture in your day-to-day life and help alleviate many pains and aliments associated with poor posture. Each check in this pose is also for good posture.
Though I always say to practice a seated pose after each standing, Dandasana is the only matching seated pose, as it engages all the Bandhas. Otherwise this is a fairly neutral pose to begin with and is not required to counter.