Look for coins with upward trending graphs, some decent market cap and above all: continued trading. Add a small spread, strong buying power and you should be good.
Solid advice, except the upward trending graph and low spreads doesn't always tell you the ideal time to buy. If you are only in it for short-term speculation, then use technical analysis at your peril. I'd prefer to recommend that investors look for an altcoin that is totally unique and has the capability to beat Bitcoin. Then buy for a no-brainer long-term investment, because you know the fundamental value. I feel very strongly such an altcoin will appear over the next months and it will stand head & shoulders above everything else.
I've bolded what I think are the high priority suggestions in your post.
I will also add that the coin should be able to prove mathematically that it was fairly launched.
I will also suggest that expropriation will begin in Europe accelerating after September and into full contagion in 2016, worsening further in 2017. So anonymity is going to be much more important feature than it is considered now.
I also suggest the decentralized scaling of the block chain and provable resistance against 51% attack and censorship will be a very important feature that afaik no existing crypto-coin has.
Disclaimer: I am formerly prolific user AnonyMint and thus I have a vested interest in strong, three letter agency middle finger anonymity and permission-less (censorship-proof) commerce. My real name is on this page of AnonyMint's archives.