It depends on the coin whether it is worth to invest in or not. If the coin has no potential then I would most probably not invest in it but if the coin has potential then I would look how low the price has gone from the past few weeks. I would understand the charts and predict how much the price would increase in future and then wait for the right moment to buy the dip. I wont put in all my money but rather invest a small amount so that I could buy more if it dips again.