According to me there are number of mistakes we do in trading which goes unnoticed most of the times. Some of them which I remember are:
1. Relying upon a Scam Broker, which means if you have not done full search before selecting a broker, your trades might be in the wrong hands.
Yes every broker is here to earn but choose one which is atleast reliable for processing proper deposit and withdrawals.
2. Dependency on Demo account. Too much reliance on the demo environment can be harmful because things like re-quotes, rejection of trades are encountered only in live account. So it would be advisable to start with demo but to know more switch to live (only with small amount open your account).
3. Investors are often fooled by the brokers about ecn brokers. Although in reality they are market makers but they potray themselves as STP or ECN brokers.