How Often Should I Pray?

I read this tonight from Martin Luther:

Luther recommends making prayer "the first business of the morning and the last at night." He says, "cultivate the habit of falling asleep with the Lord's Prayer on your lips every evening when you go to bed and again every morning when you get up. And if occasion, place, and time permit, pray before you do anything else." (p. 108 A Guide to Prayer by Rueben P. Job and Norman Shawchuck.)