Click on the picture to enlarge illustration on how subjectivity can make you go nuts. A lot of biases can be done away if the entire trading methodology is clearly defined. When you write down rules for each of your observation and beliefs it is the first step towards objective/mechanical trading. Maintaining a Journal can help a lot in being organized.
Mistake #2: Complicating Your Trading
As a common sense rule, no one wants to work for one hour if the same result can be achieved in 5 minutes. Yet traders complicate things unnecessarily. A common example is using 3-4 oscillators and looking for confirmation on each of them. This problem comes because people do not work on an indicator from scratch. If you are willing to sit down and work each of your trading ideas/methods/indicators from scratch you can find out which all have overlapping elements and appropriately eliminate them.
Mistake #3: Neglecting The Bigger-Picture Perspective
This is similar to giving too much importance to a price pattern or indicator signal without referring to immediate time frames. Refer here on how watching three time frames can have a significant improvement in your trading.
Mistake #4: Trading on Small Time Frame
Starting to trade on a time frame which does not gives you enough time to think and re-asses your trades can be stressful and expensive at the same time. Except very few people, starting with swing trading can be much more profitable than starting with daytrading.
Mistake #5: Acting On Generalizations
One-liners by intelligent people may sound effective, but they cannot be taken down as rules! Market did not appreciate world's greatest genius like Einstein, and it definitely does not like the one line generalization by your favorite trader. Examples are:
Chart Patterns do not work anymore.
Such pattern/indicator has accuracy of x%.
Its all about price action, indicators only follow price and are lagging.
Such and such method/indicator is useless.
Fundamental Analysis does not work.
Volume leads the prices.
Mistake #6: Trying to Learn TA From Analysts and Journalists
Many people with vast amount of trading related information are not able to make money through their trading. This is very common. For the thousands of trading books available on Amazon if you carefully research on the biography of authors, you will be surprised to see how few actually have trading as their primary source of income. Typical examples are Jake Bernstein and Bob Pretcher. See here for a list of trading 'gurus'.
Mistake #7: Getting Religious About a Method
Flexibility and Adaptability are the prerequisite for this game. Howsoever great a method/indicator may look, always keep working to refine it. A common example is going by the magic retracement numbers of 0.38, 0.62 etc. Sorry to disappoint, but the market does not confines to couple of rules.