Two good points by haejin here, 1) careful about buying "thinly traded" coins.
But 2) also often forgotten or overlooked is the following...
"...are two ways a /BTC pair can run. First, as BTC rises, the rate of demand for the altcoin must exceed the rate of rise for /BTC. The second is when BTC declines, this would raise just about every /BTC pair."
Beginners would do well to take notes.