On the first pitch or when cragging sigle pitch routes, it's whenever you feel like it. But think about this... if you place your first gear at 9-10 feet off the ground, then after you have climbed only about 6 feet more, with rope stretch, you are getting into groundfall territory again anyway and need to place another piece pronto. So you might as well just put in the first piece at 15 feet unless there is a hard move in between 10 and 15 feet... unless you have some other reason. The real point is is that a piece close to the ground doesn't protect you for very long so why not make a couple more moves first, until you get the scary highball feeling.
Ideally after you get the first two pieces in you can increase the distance between pieces because with more rope out your potential fall factor is reducing. Say you put in one piece at 12 feet or so and next one around 22, next one around 38, next one around 55, next one at 75, one more around 100 feet... unless there's a specific crux you want a close piece for or you want something in to keep you off a ledge or a bulge or to protect your second or whatever.
On a multipitch though, put one piece in as soon as you can off the belay so that you dn't Factor 2 onto the belay. Even if it's like 5 feet up from the belay... then go back to the strategy givn above.