I've worked in stock market data analysis and distribution (albeit it was some time ago, around the time of the 2007 crash).
Day traders are losers, literally.
There's no way you're going to be able to compete with the large trading institutions and their automated systems. These systems can react far faster to market fluctuations than you will ever be able to manually. Plus they don't incur the transaction fees and delays with brokers that you as a small time player will inevitably have to deal with.
Also, these large trading firms have access to market data that's far more accurate and up to date than what's sold (or worse yet, freely available) to the small traders in their living room or home office.
While in theory you could buy the realtime data (well, delayed by a fraction of a second to a few seconds depending on the source) but it'd be prohibitively expensive, and the cheap data is updated only once an hour or so, maybe once every 10 minutes for an intermediate plan.
For day trading, which depends on making snap decisions on rapidly fluctuating prices, that's lethal. And without a budget of many millions of dollars in ready cash to buy and even more invested already in stock, you're not going to be able to afford the more up to date data sources simply because of their price.
You're also not going to get the high speed transactions that make use of such data sources worth the cost, as you'll be dealing through brokers that typically delay your transaction a bit in order to bundle it with other transactions in order to reduce their operational cost (say you order your broker to buy 100 shares in XEDAS, he'll delay that for maybe 10 minutes in the hope of getting more orders for that stock, as his cost to place an order doesn't depend on the size of the order, only on the number of distinct instruments). That broker also will charge you fees, of course, which fees may well be higher than the return on rapidly buying and selling small amounts on minute price fluctuations, and again you won't have the money to buy large enough amounts in order to make that game yield enough income to yield more than the brokerage fees per transaction.
As a small time investor, it's far better to buy into what appears to be a stable, slowly growing, portfolio. A few transactions per month in normal times, each large enough to make the transaction fees small in comparison to the transaction size, and keep that stock long term even if the price fluctuates downward for a while (of course if it appears to be going down the drain completely, maybe because of changes that make the company unstable, sell off and reinvest in something else, but don't do so just because this morning it was 10 cents higher than it is in the afternoon).