There are many sites out there, and we cannot be 100% sure they will not be a scam or close sooner or later. As for trading technique, most people will say "buy low, sell high", but I will give you some more tips.
-New coins use to raise in price fast, then go down. You can buy a new coin and inmediately put a sell order for around 2-5% more and might get some profit (not everytime but sometimes). I guess Yobit is a good site in which many new coins show up from time to time.
-Look at the chats in trading sites. You can perceive there the interest in some coins and act accordingly.
-Check transaction volume. If a coin has no volume, you probably do not want it.
amazing advice dude, thank you very much