When I first sit down to meditate, my mind is often too busy to get into it well, so one thing I’ve learned to do is to try to meditate for about eight minutes, then get up, stretch a little bit (a few yoga stretches), then sit back down to meditate normally. My second attempt is usually significantly better than my first attempt. There are other things you can do to calm the mind, but this works well for me.
Another thing I was reminded of again today is that the quality of meditation often changes over time. Today there was something new, and I thought, “Cool ... this is different,” before getting back to the meditation at hand. For me that happens a lot, so I assume it happens for other people as well.