Make it clear which is your native (preferred) working languageYou can add other languages, of course but you should only aim to translate into your native mother tongue or the language in which you have studied and qualified in school and university. Yes, you can be a bilingual or have a high degree of proficiency in another language, but you will have to prove it. Project Managers are busy people and they need to choose native translators. I have only met a handful of translators who could perfectly translate into two languages and there was never a comeback from their output (Hungarian and Romanian, French and Spanish, and Arabic and English). Many bilinguals or translators coming from a mixed marriage are sincere and always prefer working into one language - they make very good interpreters, but not translators. Written words are scrutinized and can be read by thousands of people.
Capable of adapting to several CAT toolsThere is nothing worse for a translation company than having to deal with translators who will not learn new tools and try to work as if nothing had happened in technology in the last 20 years. If the Internet has made freelance translation services available from Tokyo and Shanghai to Berlin, Madrid, Boston, Mexico City and Sao Paulo, it means that people also have different needs. Therefore, a good freelance translator needs to be skilled in the popular CAT tools or alternatives to them. I quite like online tools because they make collaborative work easier. Desktop CAT tools were designed form translators in isolation. In times when centralized translation memory systems and machine translation APIs are available in the market, not being aware of the tools and possibilities beyond traditional translation is suicidal. Stay ahead of the pack and learn to use SmartCat, Memsource, SDL Trados, MemoQ and Wordfast.
FlexibilityAn translation company always prefers to work with freelancers who can take pressure off and make life easy. That's a general business rule. Accepting the company's payment terms and rates (as long as they are fair and not bottom low) will matter. Most companies will be happy to have freelancers to call or email first because of this. Different jobs can come with different rates from the end, direct client, or quality expectations may be different. I'm not saying the translator should cut rates down and enter the rat race, but we are all aware that volumes come with discounts. And hey! you should be able to offer both translation and benefit from postediting...More often than not, agreeing to do this makes the project manager remember you when the next job in your language pair comes along. I agree that it may not be everybody’s cup of tea, but it did help me and proved to be of invaluable help during the first year or two as a freelance translator. Be flexible with regards to different payment modes. Each organization has its own way of settling accounts: PayPal, Skrill, bank transfers. Sharing transfer costs is the norm. You will find more companies to work with if you have multiple options to accept payment.
Availability, yes availability and connectivity
Let's face it: you now run your own business, so that means being on call more hours than the typical 9-5 office job. You probably carry your email on your cell phone. And you may get emails and requests from different time zones. Such is the nature of the freelance translator life nowadays. Being available most of the times means being contacted more frequently for translation jobs. While accepting the fact you can be tied up with work when contacted for a new job, it is never a good idea to set up an automated reply declaring your unavailability unless you are on vacation ( really on vacation). Have the email open and next to you and look at it at least once an hour. Also, email may not be the only way to communicate. Some tools like SmartCat can send you warnings via Telegram and some translation agencies use twitter or Google+ to recruit translators and offer jobs.