Provide the agency with any additional documents which you deem useful. Any suggestions regarding the vocabulary choice and writing style will be helpful for the translators. You should give them an acceptable delivery date to ensure that translators can analyze and translate your documents properly. Don’t expect good quality work within a short time. Lastly, try to be available to the translator so that he can clear any confusion while working on your project. If you work in this way, you’ll surely receive high quality work from the translator.