Usually i choose the altcoins with big potential to trade and i avoid the shitty new coins. There is some known altcoins actually used by big community and their prices is increasing as well
Sometimes I also search for those coins for which will have a bigger volume of trade and which will have higher fluctuation rate, with these kind of coins I am able to earn a faster profit, but in some cases when I imagine a good profit from a coin then I do not care that this coins is new or older.