Paul that's a very good question. When I have the profits and time to look for my next venture I start by first looking at bitcointalk.org's altcoin ann(announcement) page and studying the coin info & community of new coins. Next I look at what coins have just been announced to be added to either the Poloniex exchange, Bittrex or Cryptopia. I then look those coins up on google to see what I can find or see about them.
Basic filters I use to move on past looking at a newly listed coin on an exchange is I don't usually want a coin that has been premined and is just now finding it's way on it's first real exchange. That coin will be dumped for weeks before ready to find it's true price floor. If it's an already existing coin coming from a more obscure exchange and now onto a bigger one, that's a good sign(www.coinmarketcap.com is a must info tool).
If a coin has some actual unique purpose that's a big plus but not a deal breaker for me. If the coin's team are visible meaning they have their name and picture on their website and/or bitcointalk.org announcement page that's a big plus. I hope this helps.