I've been trading for about a year now, with moderate success. Obviously, I'm still a relative newbie but have learned some VERY valuable (and expensive) lessons in my first year of trading I thought I'd share, and of course I welcome any other bits of advice from others.
I trade a very simple system, using very few indicators, mainly trend lines, support and resistance. This is mainly because the books I have read so far advocate keeping things simple, at least at first, and for the most part it has worked ok.
Lesson 1 - Stop Loss. This has been mentioned several times on this forum and I'm going to do it again, because it is so important. My ratio of picking winner vs losers is about 60:40 (60 being winners), not that great I know but as I said I still have a lot more to learn. I've done pretty well this year by my own expectations, but could have done a lot better had I made better use of stop losses earlier on. Needless to say I have learned my lesson.
Lesson 2 - Stick to your trading plan. As I said, my trading plan is pretty simple and works most of the time when I stick to it. This is a problem I had until fairly recently, thankfully no longer. I would make a plan and then change it, big mistake. Enter a trade with a plan and don't deviate from that plan!
Lesson 3 - Emotions. This is the toughest one to tackle IMO. It affects everything you do in a trade and can have disasterous affects. It affected me in several ways
>>It often stopped me executing a stop loss, thinking "I can't afford to lose this much, the price will go back up". It often didn't. I lost a lot of money this way.
>>Enter a trade for no good reason. Watching the SP go ballistic in a stock and jumping in just because your heart is racing, only to find that it then plummets. There was no plan, just driven by emotion.
>>Exiting a trade prematurely. The price has just soared in the last few days, and now has a down day. "I want out now before it goes down any more!". After a day or two the uptrend resumes and I kick myself for not following my original trading plan.
Well those are a few of my hard earned lessons from my fist year. Feel free to add some more.