The issue of trust in God is not as clear as I would like it to be.There does not seem to be any formula that you can plug in the question "In this situation should I do action or trust in God to take care of it?" The reason why there is no formula I think is that there are levels of trust. If one trust with more strength, then things work out better.
That seems to be what the Gra means in his commentary on Proverbs 3. וסוד העניין שתהפוך לבך לבטוח בה' בכל ואז יברך ה' אותך בכל.