Number 1: the Internet.
Nobody trades on the phone anymore.
You will need fast internet connection to enter orders on-line and send them to your broker, to get stock quotes from exchanges to brows world wide web and so on.
Further more, depending on your trading style you may need a backup connection, wireless perhaps, or satellite.
Markets can move fast and if you need to immediately exit a position or enter a protective order, these backup connections can come handy.
Number 2: good computer, perhaps two, with multiple monitors.
Some traders use as much as eight monitors so they can watch multiple stocks and multiple markets simultaneously.
But again it depends on your method of trading whether you need that many or not.
Number 3: residence in the day trader friendly jurisdictions.
If you live in US consider yourself lucky.
Not so much if are for example a Canadian.
Canadians cannot open an account with US brokers and have to rely on their own.
Canadian brokers are, in their turn, often charging higher commission, and otherwise may not provide an adequate service, there are simply too few of them; so if an appropriate broker is not available to you that can significantly limit your trading strategies and approaches.
Number 4: charting software.
Many traders use technical analyses to time their entries and exists.
Usually technical analyses are facilitated by special charting software, which requires installation on your computer or by online charting toolswhich you simply use in a browser.
Other software and/or online services you might need are: spreadsheets, statistical packages, and stocks scanner.
Number 5: trading capital.
Well, this one is the last on our list but not the least.
A trader if she wants to be successful has to be well capitalized.
But the good news is: if you just starting you may not need money right away.
It is a good idea to try to practice trading using a trading simulator.
The process is known as paper trading, and it is highly recommended for any novice trader as a learning method.
This list is not exhausting; there might be other things a trader needs.
If things go well and you start making money you will need to pay taxes.
So get yourself acquainted with a good tax accountant who understands specifics of a day trading business and can give a good advice.
Perhaps you also want to consider getting an advanced smart phone.
Smart phones are becoming very powerful; they now come with charting software and ability to trade off them if only your broker would support it.
It could be quite cool to leave for a coffee break and be able to monitor your positions.
It could also be used as a back up Internet connection mentioned above.
The possibilities are endless...