Often the most complicated postures are the ones we do the most. And the postures we do the most are often the ones that don't get the attention they deserve.
Although it seems like a basic pose, Warrior II is less than basic!
I could deconstruct the whole posture, but I figured I'd just tackle the hips for now.
Square the Hips?
In my experience, there's no need to "square" your hips to the long edge of your yoga mat. In most bodies when the frontal hip bones are oriented toward the long edge of your mat the front knee is forced inward and unnecessary pressure is put on the lower spine.
Play with letting your hips go where they naturally want to go. As long as your feet are in a solid foundation your hips will angle in a functional, safe manner. Most likely your frontal hip bones will slightly orientate toward the front corner of your yoga mat.
Soup Bowl Pelvis
When I was a dancer a lot of analogies and images were thrown around. The most common image was the idea of your pelvis as a soup bowl. You don't want to spill your soup forward, backward, over the sides so the image encourages the pelvis to sit in a level, "neutral" position.
Turns out the soup bowl image is also really helpful in yoga!
In Warrior II play with keeping your frontal hip bones level to each other. In other words, keep the right and left hip bones parallel to the floor. If one hip is too high the soup would spill out the side. As one hip sitting higher than the other won't add a tremendous amount of stress to the spine or pelvis I'm actually not too concerned with this aspect of the posture, but it's something worth considering in your practice.
Still using the soup bowl image, there's a slight pull of your frontal hip bones up toward your lower ribs to prevent the soup from spilling forward over the front of the pelvis. The opposite, soup spilling out the backside of the pelvis, is a less common occurrence, however, something to still consider in your own posture.
To give you a better idea and more clarity, I put together a short video for you! Check it out!