Started with 0 background in finance 5 years ago. Made a lot of money and I thought I was really good, but I was only lucky. Gave back almost all the money I made, but ALWAYS preserved my original account. Now luck is no longer a factor in my trading. My gains are smaller, but so is my risk. Trading is a fun job, but still a job...not going to be happy when I make money or sad when I lose money.
Some lessons learned in no particular order of importance:
1) To have an ego in the market is very expen$ive, you must decide if for you it is more important to be right or to make money.
2) It takes a lot of money to make little money...in other words day trading and making money fast might work for professionals, but never for the regualr guy.
3) Just because "investors" don't bet on the ponies they think that they are actually investing/trading, but they are just gambling. Unless you have an edge you are a gambler.
4) To keep your emotions out, you need a system even if it is for a longer time frame or even if it helps you to catch basic trends. Even if it is a simple mechanical system, but then again 99% of people do not have the discipline to follow their system. The thing, is that there is no point in trying to predict where the market will go tomorrow, no one can do that consistently.
5) Trading for a living is not a sprint, but a marathon. Unless you have the right psychology you will burn out, it is only a matter of time. Trading should let you buy the time to do OTHER things you want to do in your life. When your trading life is interfering with your personal life it's bad -very bad.
6) There is a HUGE industry trying to tell you about a product to BUY, a newsletter to subscribe, a secret to be discovered as long as you pay the $19.99 (or more). Guess what ? There are no financial gurus. No one knows anything and even if they say they know they still don't. No book, person or website will tell you exactly how to make money. This industry loves to bank on your HOPE to make money. Period.
7) Even if you read forums or people warn you about lessons or mistakes ultimately you will ignore them and you will make all the mistakes on your account. Your only objective is not to blow up your account while you going trough the learning curve. Your FIRST objective should not be to make money. As long as you have money you are always in time to make money. Totally OK! if you go flat/lose some for several months.
8) This is a full time job, either you do it or you don't. As many people say it takes 10+ years to become an expert at anything. Also one of the biggest reasons why traders fail is because they are undercapitalized, just like any other business. If you don't have money don't trade !
Everything written above is nothing more than my personal opinion. I am sure there is much more, but so far such principles helped me to become a full time trader.