@shibao
If you get to the end of your session and find that you've been daydreaming, or thinking about work, or running through weekend plans, and you've forgotten all about focusing on your breath, take it as a lesson. Thoughts are powerful, your mind's natural tendency is to think. Note this and resolve to "do better" next time.
Practice every day. I spend 15 minutes meditating. Even 10 minutes can be a good starting point. More serious practitioners spend 30 or 45 minutes daily. Don't try to start there. Like any exercise, it takes time to work. The most important thing is to make a habit of practicing daily.