Being computer savvy : An efficient laptop/desktop is the first thing you will need to be a professional writer. If you are reading this, you probably have one. I know of writers who still turn in handwritten manuscripts and articles - sadly, it doesn't work for most people. Work on your typing skills and have the nitty gritties of MS Office on your fingertips. Believe me, writing and editing becomes a lot easier and faster when you know your way around the features and applications.
A high-speed internet connection: I say high speed because you will need to do considerable amount of research and reading-up to write on any assigned topic (unless you don't mind running a google seahttp://www.blogger.com/img/blank.gifrch and coming back to it after lunch). Clients will expect you to be prompt with your responses, you will need to send out several emails everyday, download a lot of stuff, be efficient with your communications and possibly even maintain a website. It makes lot of sense to spend a few extra bucks on a plan that gives you good speed and unlimited usage options. Make the search engine your best friend - everything you need to know is out there.
A printer/scanner/copier: Although this is not absolutely necessary in the beginning but as you go along, you will need to send signed invoices and maintain a copy for your own record. As the volume of your work increases, you will find that it is actually more economical to have your own 3-in-one than keep running around to get it done from shops. You can regularly scan your articles published in print and present them as part of your portfolio.
A dedicated phone connection: A telephonic conversation means a lot more than an impersonal email. It establishes your credibility as a professional and allows you to connect with your clients on a 'real' basis. Provide a phone number in all your professional correspondences and make yourself available on it - it can make a deal or break it.
Business cards: Most writers don't think of this as necessary but a business card is an easy and inexpensive way to keep up your 'recall value' among clients. They are especially useful in word-of-mouth recommendations (an old client can easily hand over your contact details to a prospective one. If you live in a major city in India, you may find writing opportunities floating all around you - it certainly helps to have a business card handy.
Books that help: Most writers love to read and almost everyone (writer or not) has a dictionary at home. But when write for a living, you will need a tad more than that. Invest in style guides, thesauruses, books containing idioms and phrases, slang dictionaries and grammar tools. Oxford has a very useful 3-in-one set (I personally use it)and I even ordered one from Reader's Digest (haven't gone through it yet but it looks promising too). You will be surprised how much these books help in avoiding annoyingly cliche expressions and keeping your language fresh. Also, good writers very often bend and break the rules of grammar - you can do that only when you know them inside out!