Keep them short. Almost all prayers in the Bible were brief. Conversely, hypocrites think they will be heard for their much speaking. See what Jesus had to say about such babbling in (Matthew 6:7).
Don’t yell, scream, whoop, howl, or holler. Pagans think they will be heard for their loud prayers. The Baal-worshippers on Mount Carmel are the poster children for this foolishness. (See I Kings 18:26)
Don’t pontificate. The overly religious think they will be heard for their pious words. They just pile scriptural phrases on top of scriptural phrases and use weird words outside of their normal vocabulary. God is not impressed with that sort of thing. See what (Ecclesiastes 5:2-3) has to say about this affliction.
In Scripture, the length of one’s prayer seems to be irrelevant. Measuring our prayers (by time, the volume of one’s voice, pious words, the length, etc) is an exercise in futility and ranks as the ultimate in silliness.
When the sweetheart goes into her house at night, she does not gauge the depth of her boyfriends love by the length of his monologue.
Just talk to God. Just talk.
Be Authentic. Transparent.
Be real. Not pious.
The thief on the cross uttered a nine word prayer, “Lord, remember me when You come to Your Kingdom.” Jesus accepted this prayer and told him, “Today you’ll be with me in paradise” (Luke 23:42-43). One thing I love about this prayer is that it confirms a short, fervent prayer can change one's entire destiny even at life’s last minute!
As a new believer I would often pray softly throughout the day. And, with a new believer’s imperfect understanding, I refused to speak a final ‘amen’ because I that felt like I was ending the prayer and closing the door of communication with God, and I wanted Him to be with me all day long and to be able to pray to Him at any time.
After thirty three years of walking with Him, I still feel the same way.