Expect to get distracted a lot, like your mind wandering continuously. The key here is to observe that happening, and gently bring yourself back to your breath. Don't let it frustrate or discourage you. Watching yourself become distracted and gently bringing yourself back is part of the process of meditating, not some sign that you're failing at it. The noticing of the distraction is in itself mindfulness.

As Jon Kabat-Zinn suggests, you need to approach this with non-judgmental moment-to-moment awareness.