When dealing with external distractions in prayers, it may be easier to remove yourself from what is distracting you. As far as internal distractions go, it is much more difficult to get your mind back onto the right track once you have lost focus.
You prepare yourself when you have school or work in the morning. To do so you sleep early because you know that you need to be up at a certain time. Similarly, if you know that you have a presentation, you will go into the presentation with your materials ready and your mind focused.
It should be the same way when it comes time to your prayers. You should internally prepare yourself to stand in front of God.
Internal distractions for instance can include thoughts about what you were just watching on TV prior to praying, or the food you have in the oven. Things of that nature take your focus away from what really matters.
Do not take for granted that God knows your true intentions just because you perform the act of prayer. If your mind and focus is not invested in prayer, it means that you may not have done your prayers correctly. Simply doing the act is not enough. Internally having your mind, heart, and focus on God is the best way to enter your prayers and to complete them.