Hashem does not need our praise. He knows our needs without our telling Him. He can read our thoughts. Why, then, do we need to daven? Through tefillah, we realize the greatness of Hashem and how dependent we are upon Him every second of our lives. As we daven, we come closer to Hashem and thereby become more deserving that He should accept and answer our tefillos.
The most important thing about davening is to remember that there is someone listening. Although Hashem does not speak to us, He hears every bracha and tefillah.