I can only add my 2 cents to what others have already added wisely.
Your trading system should have some loose bigger rules such as how much you can lose in a day before you stop, whats your max loss on each trade, preserve capital etc. There are plenty of posts on this and this should be your first step.
When you make your system or follow one know your strengths and weaknesses. I find it hard to trade slow grind up days-I either avoid them or once I enter the trade I put a bracket and go watch a movie on tv. Its not my strength and I always make a mistake if I check it every 2 minutes. Trading is "always" improvising and improving--this doesnt mean you change your methodology on the fly but based on solid concrete evidence.
Keep a journal. This cannot be stressed enough--I still read journals from 2004, 2005 and see what worked then and what works now and how I have changed.
Its a game of probabilities. Every trade is random with an equal chance of success or failure no matter what your system predicted. Its hard for a lot of traders to wrap their heads around this but the sooner you "get it" the better.
ALWAYS preserve capital no matter what-If a market goes horribly wrong against you just exit. Live to fight another day. PLenty of people got wiped out by flash crash, crash of 1997 etc even though market came back same day or a couple of days later.
I tested a lot of oscillators, moving averages and plenty of other things and plenty of other peoples systems and after 10 years I can tell you the best system is the one you make yourself, for yourself. What works for me is candlesticks and it took literally 10,000's of charts of seeing how they behave. And I found out that candlesticks dont work the same as reading candlestick definitions from websites. Each candlestick is a story told.
Pick one market, become good at it and become profitable. Spend time picking the market, pros and cons. If you cant trade one market profitably, then changing markets wont help you. Also pick a system that will work in almost all kinds of markets-low volatility, high volatility, choppy, trending etc