Welcome back!
Most people who want to start a career in day trading, or simply learn it as a hobby always concentrate on the entries. “If I can just figure out the perfect entry, making money will be a piece of cake.” It always looks easy in hindsight - you enter at price X, but then the stock moves against you, and you see obviously you should have waited for Y to happen etc. This leads you down the path to try to perfect your entry for day trading. So you buy some books, take some seminars, look for the perfect “indicators” to help you in your goal of perfection (or at least as close as you can get to it). The entry actually has only a small amount to do with whether you actually are profitable or not - most of it is money management coupled with trading skills learned over time.
A first thing you need to consider when day trading is the relative volatility of the stock - the higher the volatility, the higher the odds are you will not be that great on the entry. No matter how good you are, the more crazy a stock is the easier it will have to move against you. This is not always a bad thing, it just makes you have to average into the position when day trading. So you take your position size you want, and if the stock is too volatile, look at a 5 min intra-day chart and eyeball how much it can move in 10 minutes high to low. If this number is above 2-3%, odds are you should consider averaging in. All this means is you do a partial fill where you think you should be long or short, then plan on adding the rest of the position at a more favorable price. If the stock happens to move immediately in your favor, you ride what you have and take the money - that is just how it goes.
The second thing most people do wrong when day trading, is they figure out how much they want to make on a trade, and how much it might move. They then use this dollar gain they expect to size the position. This is 100% wrong. You cannot control how much a stock goes up (or down if short). The only exact control you have is RISK - meaning your stop point. The stock might go up 0.10, might go up 10.00. The only control you have is where you cut off your loss. This is where you size your position from, not a fantasy about how much money you want to make. Its all about how much will I lose if I am dead wrong? This number should normally not be more than about 2% of your account size, most people try to keep it lower than that if they can. So figure out where your stop would be, figure out how many points that is, then figure out how much 2% max of your account is, then do the math and you have your position size.