1. You don't know how to do it.
You know how to talk, don't you? That's what prayer is -- talking to God, and learning how to listen. Like any conversation, it feels awkward if you are more or less strangers, or if you've been away for a while, but prayer is something that everyone can learn. Try some Ignatian Spirituality for some gentle, practical advice on how to get the conversation going.
2. It seems childish.
Religion seems childish to people who stopped learning about religion when they were children. Don't think that whatever you learned about God in second grade is all there is to learn! Read some Aquinas, or learn about the martyrs, and then get back to me about this "religion is childish" thing.
Keep it quick, then. Just don't skip it altogether. Are you really going to say, "I don't have 6-10 minutes to spare today? I'm planning to use 100% of my waking time wisely and well, and so I truly don't have any time at all to make a morning offering, thank God for a tasty sandwich, or mutter an apology for doing something crummy?"
4. You're mad at God.
Go ahead and tell Him, then. He can take it (He's dealt with worse). He'd rather hear that than hear nothing. And yelling at God sometimes helps us clarify, in our own minds, what, exactly, we're upset about. Sometimes what feels like anger is really heartbreak or fear.
5. You're afraid of God.
Well, maybe you should be. Maybe all of us should be, a little more often. But it should be a fear that makes us stop and look clearly at ourselves, not a fear that paralyzes us and makes us hide. When we start by fearing God, we often go on to a greater awareness of our own need for God's love and mercy and pity -- which are in greater supply than His wrath.
6. You pray so badly, it seems pointless.
Frankly, you'd be a lot worse off if you were proud of how skillfully and effectively you pray. God is not a vending machine who will dispense the desired product if you put the right coins in. He's Someone -- someone who is listening, hanging on your every word. He loves you, and wants the best for you. He's the one who makes prayer worthwhile and efficacious, not you. Mostly all you have to do is show up, and He does the rest.
7. You're not sure it has any effect.
Well, it might not have the effect you're hoping for. But if you think praying has no effect, then look at what your life looks like when you don't pray -- don't make contact with God, don't ask for and look for His grace and help, don't work on the ongoing conversion of your heart. Sometimes, regular prayer is like oxygen: you may not notice what it's doing for you, but you sure miss it if it goes away.
8. You feel insincere.
Don't worry about it. There's no possible way of fooling God into thinking you're somebody that you're not. He knows you better than you know yourself -- and that means He knows good and worthy things about you that even you don't suspect, or aren't able to acknowledge. If you can't sincerely praise or glorify God or repent of your sin and really mean it, then just add a sheepish acknowledgement of that fact, and ask for a boost until you do mean it.
9. You don't like that flowery language.
That's okay. A lot of Catholic culture is just that: culture. You can just talk to God in your own language.
10. You're not sure He's listening.
Well, if he's not, you haven't lost anything by trying! But do give it a try. Advent is almost here. Why not make a resolution to pray every single day until Christmas, and see what happens?