First, I look at serving size, then I look at calories. If the ratio of calories to serving size does not look good...I reject the item.
Next, I look at the bad stuff: saturated fat, sugar and sodium. If these are off the charts, then good bye!
Then, I look at nutrition. I look for the percentage of daily value of something good in a serving of that food! It is amazing how many packaged foods have no nutritional value whatsoever. But if there is fiber, 100% vitamin C, or a good amount of Zinc, Calcium, and so on, then I might choose the item as a part of a more complete meal.
Sometimes, I will compare an item's nutritional value against the competitor's versions to see which company has the better product.
After that, I'm done.