I think the most common time frame in forex is when we are doing the tradings with big time frame. Most of the bigger time frames are giving the good picture of the market and we can predit well.I used higher time frame to see the true trend when i trade with scalping. If you are a short term trader, you must use the frame of 5 or 15 minutes to have the best performance in your trading. On the other hand, the trader must not make the mistake of operating without enough have been prepared in forex. In other words, if you were not successful in demo accounts, then you should not waste time and money by trading in real accounts.