With STAR Voting honesty is the best policy. The best strategy is to give your favorite or favorites a full 5 stars and to use your scores to show your preferences between the other candidates.
While there are some hypothetical scenarios where you might get an edge by putting down higher or lower scores for various candidates, in practice there is no way to know when this might help and when it would hurt. This kind of dishonest voting is more likely to backfire so it’s not a good strategy.
You can read a more technical comparison of strategic incentives in various systems here.