There isn't a "proper" strategy just for buying altcoins, the only "rule" that i follow is just buy those who have a really nice roadmap. Just take a look over Envion & Pivx
I like those alts, Pivx is probably the main altcoin that i am buying right now, i just started buying this coin two days ago when the price was about $8,50 each one of them.
Now i am a lucky guy, because the price decreased to $7,75, so i am still buying at a cheaper rate than before.
And Envion is a good ico, i really like those guys, and they have already raised more than 34 million dollars, that is an incredible result just for the first stage of their ico.
Anyway, there isn't any strategy to follow, i support this guy, but there are some patterns that you can easily follow from other people than might be able to help you out to make a better trade.