Useful for beginners, but I often do this in lieu of counting breaths:

• Breath naturally and easily through the nose.
• Note the vedana of the sense of smell about once every second (e.g., "neutral ... neutral ... pleasant ... pleasant ... neutral ... pleasant ... pleasant ... pleasant ... pleasant ...")

That's it. I found the practice by accident one day. I forgot to take down the garbage. About two or three minutes into my sitting practice, I realized, "What the hell is that smell?" I decided to just go with it.

Enjoy.