There seem to be two different ways in which meditation is commonly approached. It's not a clean divide, but I'll turn them into distinct categories for this post.
1. Psychological / spiritual
It's odd to lump these together, but the scientific study of meditation seems to be largely based in practices that many would consider "spiritual." This includes things like breathing practices and yoga, to calm the body and mind.
I think it commonly looks like this:
I know it's probably obnoxious of me to do so, but I can't help but laugh at pictures like that. Those people are, like, so much more groovy than me. It's like they're making gang signs. Of spirituality.
This is the approach that many are trying to secularize, so that you don't have to wear particular clothing or beads, or have a cool-looking silhouette, or rub a fat man's belly.
2. As an introduction to awareness
Some traditions (particularly the ones that call themselves "non-dual") suggest that meditation is primarily a way of calming your mind just enough to recognize "awareness": the
knowing faculty of the mind. It's the thing (or non-thing) by which you experience anything at all. Once you recognize it, the idea is to make that recognition deep and continuous.
Some suggest you do it by invoking various
deities. Others say it's as simple as "
short moments, repeated many times." I prefer the latter approach. Relax and be cognizant. When
everything is gone, what's left is awareness. Even when everything is there, what's underneath, inside, and all around, is awareness. As the recognition of awareness grows, the division between (and the need for) the absence or presence of any particular experience fades away.
Sometimes I feel it's just too simple, and so I think I have to go back to one of the more "complicated" approaches (deities, breathing exercises). But all of the awareness traditions tell you that when it's done right, it does in fact feel "too simple."
Its simplicity is also a trap. If there are no explicit signs to indicate that you're doing it "right," you can easily fall into solipsism or nihilism or some other -ism. Or maybe you think "screw meditation, I'm beyond that," even though you're not beyond anything at all.
So how do you know? I think it's just that when you know, you know. Yeah, that's not helpful, but I'm not really trying to teach anything anyway ;)
In the end, obviously, people should do whatever works best for them. But at some point, if you feel that all this "meditation" stuff is too contrived or spiritual or constrictive, consider that there's another way.