here are some suggestions:
1. Play it in defense if you can, it's easier to hit the desirable target this way since your Primal will likely block 2 or more targets.
2. Don't play it on turn 5, it's an obvious play from 2wp, especially when the other player has a few large units on board.
3. Think about the unit placement that your opponent is most likely to use i.e: Packleader at the end of the assault zone.
4. Try to assess the board and your opponent's actions, ask yourself: Will he hold back this turn (because my board presence is so intimidating? Or is he likely to play offensively since he assumes he has the board.