Everything we say and do either honors or dishonors our heavenly Father. We honor Him by our obedience, worship, and love. We dishonor His name when we curse or take His name in vain. A habit of saying such things as "Oh Lord" or "Oh my God" as exclamations take His name in vain and are not honoring to Him.
To "hallow" God's name when we begin to pray, I think it's important to realize that our loving Father is mighty and holy. Reviewing the names of God that He has revealed in Scripture help us to know His character, such as: The Lord Who Heals, The God Who Sees, The Creator, God Most High, The Lord Our Righteousness, etc.