It gets easier if you can focus on a few key points to help you with your balance. I think the following three points are the most important to begin with:
- Balanced weight under feet. All four corners need to press evenly while lifting the arches. This is the most important point! The foundation of the pose needs to be strong and firm. The feet are the foundation of the standing poses, and if they're not working properly then the rest of the pose won't work as well. The weight needs to be evenly distributed on each foot -- between the heel and the ball of the foot, and between inner and the outer foot. Or you can think about the "four corners of the feet": base of the big toe, base of the little toe, inner heel and outer heel.
- Extended spine and lifted, open chest.
- Steady, quiet gaze.
- Strong, extended legs in poses where the legs are straight.
- Stable pelvis
- Strong, extended arms in poses where the arms are straight.
Tadasana (mountain pose)
Often we take the weight forward when we stand upright, and our toes grip the floor. Take enough weight back into the heels so that you are able to lift the toes. But do this while still keeping the base of the big toe and the inner heel pressing. Lifting the toes while pressing down the four corners of the foot will help you to find the lift of the arch of the foot. Keep the arch lifting, and let the toes release back to the floor.
Now as you press down evenly through your feet, lift and broaden your chest, keeping your gaze steady and level. If your chest isn't lifted or your gaze wavers, there's less steadiness in the pose even if your feet are working well.
For the secondary points: the action of pressing down through the feet starts to bring about the proper extension and stability of the legs. When the legs are working well, then there's more stability in the pelvis. Firm, or grip, the outer upper thighs into the bone, and lengthen the buttocks to bring the pelvis into a stable upright, neutral position. Extending the arms, with shoulders rolled back, will assist you in lifting the chest.
Note the strong vertical extension of the whole body -- rooting down into the floor through the feet and the extension upward through the lifted chest and the crown of the head.
Now take the information that you learned in Tadasana and apply it to the following poses.
Vrksasana (Tree pose)
There's the tendency for many of us to roll to the outer edge and front of the standing foot in Vrksasana. To bring the weigh evenly under the four corners of the foot, press down through the base of the big toe while lifting the arch. Don't grip the toes down, but take enough weight back into the heel to let the toes rest down. Strongly lift the chest and keep the gaze steady and calm.
The foot of the lifted leg also presses evenly into the standing leg thigh. Stabilize the pelvis by pressing the standing leg thigh back into the lifted foot. Keep the buttocks down as you continue to lift the chest.
The strong upward extension of the arms will help with the lift of the chest. You've seen people doing this pose with the arms over the head, palms together and elbows bent. This is still a "pretty" looking pose, but unless the arms are extended (i.e. "straight"), they won't assist in the balance of the pose. That's why we often do this pose with the arms separated -- because it's more likely that we can straighten the arms.
Utthita trikonasana (Triangle pose)
So, two good points of awareness to bring more stability to this pose are to press the base of the big toe down on the front leg, while still completely turning the leg from the hip socket, and press back and down through the outer heel on the back leg. From this stable pressing through the feet, extend the legs and firm the outer upper thighs into the thigh bone. Lengthen the buttocks away from the waist, and lengthen the chest in the opposite direction. The strong extension of the arms help open the chest as well as give more stability to the trunk.
Ardha chandrasana (Half-moon pose)
Virabhadrasana I (Warrior pose 1)
Without this awareness of the back foot pressing, the arch of this foot collapses, and the leg doesn't give us much stability. Without the lift of the arms and chest, the low back collapses.
Practice the awareness of these points in other standing poses including balance poses such as Garudhasana, Virabhadrasana III, and Utthita hasta padangusthasana (your homework also includes figuring out what these poses are!). Start with the base and work up through the legs, lifting the chest, and keep the gaze steady.
And do practice! You can intellectually understand how these points will help you balance better, but the poses still won't come until you do practice them!