A successful is that you buy bitcoin with lower price and sell them little higher and get some benefit from it.
but every exchange site have different exchanging system you should know that how they works. localbitcoin is a different type of site, it is actually a exchanging site but exchanges are not controlled by site's staff, there users can set their own price and rates, so try to nearest person you and try to cheapest rate for bitcoin.
Tip: if you trade in bitcointalk forum, make sure to user escrow for success your trade.
this is true. never ever buy a bitcoin in a higher price then sell it in a lower price. you should know when is the right time to buy and you should also know when to sell your bitcoins. after doing so. i suggest you invest more bitcoins, the larger amount of bitcoin the larger profit. but be cautious when selling. some sites has a different parameters in bitcoins.