Gee, this question gets asked so regularly (and to be honest, most who ask it - fail - and disappear from Hot Copper), it is a really difficult thing to do.
There is so much to learn about trading the markets, so be patient, don't rush, don't force trades, let the trades come to you (sometimes less is more).
Don't revenge trade, don't take on too much risk.
Take a break when you need to, and leave your bravado at the door when you turn on the trading computer.
Educate yourself about all aspects of trading and the markets, and be prepared for this to take some time.
Develop a trading plan, with rules you can stick to (and then stick to them).
Personally, I think that the shorter the timeframe, the more difficult it is - day trading is difficult !!
Start off with really small positions, and aim to trade trade consistantly for a decent period of time without blowing up your account (going broke), then you can consider increasing your positions, especially if you can actually turn a profit. Don't rush it, the markets will always be there.
Don't expect that trading will be easy (if it was easy, everyone would be doing it), it is hard and time consuming work.
Learn a little bit about all the different types of Technical Analysis (TA) and find the one which appeals to you the most (the one which makes the most sense), and then learn it thoroughly (become a master at it). This will take some time, especially from a cold start (probably a couple of years).
Money management and risk management are by far the most important skills to learn, if you lose all your capital, you can't come back and trade tomorrow - stay in the game.
As a trader, you will be pitting yourself against other market professionals, and given the opportunity, they will attempt to wrong foot you, and take your money without blinking. Learn to manage your trading account.
You need to become a bit of an all rounder, a stock selector, a chart reader, a trader, a money manager - all these are individual skills that need to be learned.
Try to find out where your personality and character are best suited in the markets, as you may be better suited to short term trading, and not actual day trading.
You may 'want' to be a day trader, but that is no good if that is not where you are best suited. This may take some time (and cost some money) to do.
Start following sharks37 (and go through some of his history using the advanced search function) , he spends most of his time in the Forex forum, but also trades stocks. He is very approachable, and extremely dedicated to trading (he turned professional about a year or 18 months ago). He has a science background, so is very analytical, but most importantly he is a bit like you (just more advanced), he had been involved in the markets previously (so had some prior knowledge), and is now trading more seriously (professionally).
There are quite a few more posters who would be of value to follow, but probably best to start off slowly, and add some more a bit later on, if you try to take in too much too quickly, it is unlikely you will learn and understand it properly.
Do you have a realistic time frame to achieve your goal of day trading ??
Just remember - many try to do this, and most fail, day trading is a really hard thing to do successfully over time (and in all types of markets), it takes real skill.
cheers
PS- Once you know the stock you will trade, you will find that entries are the most important part of the trade. Getting the entry right will make it much more difficult to lose money (always possible, just more difficult).
