It’s better to start with destroying the boxes, though it’s not necessary to focus on removing all of them.
After you’ve cleared most of the boxes, start creating as many power-ups as possible. Explode them together but save your Rainbow Blasts and try to use two Rainbow Blasts together. If you get an opportunity to explode a power-up close to the left or right side of the field and hit the columns on the left and right, try not to miss it.
Aside from collecting emeralds, you need to collect 7 lemonades as well. Remember that only 2 lemonades can be present on the field at the same time. After you collect a lemonade, make matches as low as possible to cause multiple auto-matches above to follow.