Simple, wonderful advice on prayer from Jean-Pierre de Caussade:
I have only two things to say on the subject of prayer:
Make it with absolute compliance with the will of God, no matter whether it be successful, or you are troubled with dryness, distractions, or other obstacles.
If it is easy and full of consolations, return thanks to God without dwelling on the pleasure it has caused you.
If it has not succeeded, submit to God, humbling yourself, and go away contented and in peace even if it should have failed through your own fault; redoubling your confidence and resignation to his holy will.
Persevere in this way and sooner or later God will give you grace to pray properly.
But whatever trials you may have to endure, never allow yourselves to be discouraged.