Read Marta's Business School blog. Attend her school if you want a kick-start, but it'll still be useful if you've been around for a couple of years. Get her e-book about CVs, and some basics about social media. Watch her wonderful Traduemprende presentation about the Blue Ocean strategy and how it applies to you as a freelance translator. She's working on a book right now. You should probably read it. The list of contents looks promising.
If you're still new, reading these books can make sense:
The Prosperous Translator — Advice from Fire Ant & Worker Bee by Chris Durban
How to Succeed as a Freelance Translator and Thoughts on Translation by Corinne McKay (also an interesting blog on the site).
The Entrepreneurial Linguist by Judy and Dagmar Jenner (check out the blog too).
Some are available as e-books, others can be ordered online, preferably somewhere close to where you live. They aren't expensive, you're basically paying $10-$25 plus time reading for potentially useful knowledge and inspiration. Inspiration may be just as important as knowledge.
Read about Blue Ocean strategy concepts at source. There are even business strategising tools there if you have the head or heart for that. Plus a library with articles.
Read or listen, or both in some cases, to Ed Gandia (who went from 0 to six figures in 27 months as a business writer/copywriter) for some quality stuff the freelance translation sector has not yet discovered.
Get Alastaire Allday's Think Like a Copywriter e-book. If you don't do marketing translation or translate high-quality writing, at least it'll help you handle your online presentation. His blog is nice to read, too. Get other books. Including some tips from a murder convict turned copywriter (thanks to Ben Locker and Associates for digging it up).
You need copywriting for two reasons: to translate copy for others (or transcreate, or translate image-sensitive materials), and to write the copy for yourself.
Before you plunge yourself into 'writing that sells', get a hang of writing correctly, which includes clarity and brevity and sets the canvas for writing really well. For no-nonsense English reference, get Grammar Rules by Craig Shrives, who created Grammar Monster. For King's English, go back to 1908.
Take writing courses in person or online. Creative writing, business writing, legal writing, medical writing, whatever floats your boat. I have a hunch they look good on CVs and raise your profile. And they differentiate you.
Look at Websites for Translators. In short, for Ł775 they'll do your website, logo, CV and business card, which is frankly not a bad deal. Consider that time is money, and DIY takes a lot of time. Their portfolio contains some inspiration if you do go DIY, plus, you can see if you're happy with their quality. I preferred DIY because I have a web design background, but I check out their projects from time to time.
Get certifications. Whatever it costs to get certified, it'll probably pay back better than if you put the some money in advertising. Those things are often valid a lifetime.
Rely on word of mouth and testimonials. There is no better marketing or advertising than happy clients, so make them happy. When they are happy, ask them to leave testimonials for you. It is easier to retain existing clients than to make new ones, so take good care of those you already have.
Don't undersell. Get a hang of what your work is worth or how high it can really sell, but you also need to know how much you need to earn. Your annual projected costs, taxes, bills, continued education, investments, savings and cash in bank divided by the number of hours you spend translating should give you a ballpark figure of effective hourly rate. Then calculate how much you can translate within one hour. Calculate how much you need to make per word accordingly.
Be smarter than competing on price, which is a race to the bottom,, and don't be lazy. Getting new contacts takes a lot of footwork, such as writing to 100 addresses on a single day to get 5 replies, this is normal. Try to fill your calendar with work you like, work that pays, but don't expect your calendar to become full, nor does it need to be. But if you prefer to cut your prices rather than spending time and money on marketing, that's still a legitimate strategy, just don't make it your long term.
Remember that if you're going to earn $300 no matter what, it's better to translate 10 pages at $30 per than 30 pages for $10 each. You need experience and referrals? Work pro bono for charities and non-government organisations but keep your rates up for business clients. You'll still have earned the same money and spent the same time but will have good-looking testimonials from NGO's who won't begrudge you the referrals and tell you to keep the work secret like some agencies or even clients may do.
Your website potentially has more space than you can fill, so use it. As long as you write well, you can write everything you want your clients to know, and add pictures. On your own terms.
In short, be good, be different, know how to write your story and make it read. Convince readers, do business with the convinced, keep them happy so they're coming back for more and bringing their friends along.