We can meditate in any number of ways. Probably more that I know or could mention to list.

As long as they are Christian meditation and do not borrow potentially dangerous practices from other kinds of thought, and as long as we do not allow pride or deception to creep in (this can be easy or extremely difficult, depending on the degree) ... then all of them are good. It can be that certain ones are better suited to certain times or persons.
Meditating on Scripture is basic. Taking a very short passage, usually, with only one principle to it (anywhere from a few verses to just a phrase, depending on the passage). Turning it over in the mind, praying to God to reveal its truth to our heart, thinking how we might apply it, getting deeply into exactly what the original words are saying, simply delighting in it and thanking God. It depends on the passage.
Meditation in prayer is also good. These are often short prayers such as the Jesus Prayer, a brief line from a Psalm, or sometimes a line (or line by line) from a formal prayer, like the Lord's Prayer. The key is to FOCUS on the words, their meaning, letting them seep into your spirit. If done in this way, it is not "vain repetition" but very fruitful. Letting your mind babble the words with no attention whatsoever, thinking you are praying, would be another matter. (Though there is such a thing as demonically inspired distraction, which we may face at times.)
There is also a still, silent contemplation, a meditation upon the presence of God (as far as we can know Him as limited creatures), a waiting upon the Lord. This can be very fruitful, and very profound. It is also the most potentially dangerous I've mentioned thus far.
Another very helpful kind of meditation is to be aware of God in all things, see His hand in all of creation, rejoice in constant thanks and awareness of what He has created and done. This often takes some effort and maturity to sustain, but can be practiced by anyone. Sometimes children are even better at it than adults.

And is in every way beneficial (just don't let it mix with pantheistic ideas of everything BEING God, just because God created all things and is everywhere present).
Like I said, I'm sure there are more. These are the major practices that come to mind though.