Meditation help - Am i observing a thought like I should or entertaining it?

I have a question with how to properly meditate, and a quick glance at other questions at this site seem to indicate I believe this exchange can provide answers. I have two questions: 1) When I meditate, I often find myself daydreaming more than having thoughts bother me, although I can very occasionally find myself daydreaming of something in my past that was unpleasant (doesn't seem to happen much though). To simply observe this thought, do I let it play out or try and focus on my breathing? 2) I have some symptoms of OCD, such as the whim of my internal voice at times playing out an uncomfortable experience in my head or a statement that bothers me (which is why my mind states it), and I worry if I don't address I might subconsciously believe it. (Such as, if the compulsive thought that bothered me was "I'm a bad person" and if I just let that sit with me instead of addressing it, merely observe it, I might subconsciously believe it. This is just an example but it illustrates what I'm getting at). Can I rest assured just observing such a thought won't cause such subconscious beliefs?