The world will be taken care of automatically, as the root will take care of all the branches and the leaves and fruits. God first, the world next, yourself last. This is what Swami Sivanandaji Maharaj used to say the cause first, the effect afterwards. The first is the largest, inclusive of what is produced, and inclusive of yourself. Meditation is our duty.
Nothing can be more profitable for a person than to be one's own self.
To thine own self be true. To be true to everything else except to your own self, is not of any avail. You can concentrate on God, wherever God be, according to you. God is somewhere, and on that you meditate. Each one has to choose one's own point of concentration according to one's understanding and predilection.