Some preliminary work is surely needed. The following points immediately come to my mind:

1. Keep a list (to be constantly updated) of all technical terms and be sure that you discuss a unitary translation before completing your part.
2. Be sure you agree about the style of your translation. I, to begin with, use (round) parentheses for explanations and Sanskrit terms and [square] brackets for additions of words which are not found in the Sanskrit although they could have been there. E.g. nagaraṃ gacchāmi “I go to the city” (No need to put “I” in brackets, since it is already included in gacchāmi, same applies to “to the”). But kaiścid bhedo uktaḥ viṣayāntarāt “Some said that the difference [between Linguistic Communication and inference] is due to the fact that they have a different object” (since the author could have spelt out the elements which are different, but decided not to do so).
3. Be sure you agree about the purpose of your translation. As far as philosophical texts are concerned, for instance, I aim at being understandable while not camouflaging the style of the author. In other words, I would add several explanations in brackets if the text just presuposses things unknown to Western readers (e.g., that “Śyena” is the name of a malefic sacrifice), but I would not make the text sound as if it had been written yesterday in Austin (this is also one of the reasons, IMHO, for avoiding translations such as “inference to the best explanation” for arthāpatti).
4. Closely connected to the above is an agreement concerning one’s target reader. Kataoka 2011, for instance, clearly envisions a targer reader who knows Sanskrit and uses the translation as a guide through the text.
5. All translations of Sanskrit texts need an accurate introduction and/or footnotes and/or glosses and/or…. Be sure that you agree about how to use each of these tools (Should the introductory study explain all and make the following Sanskrit text understandable as in Freschi 2012? Should the introductory text show the philosophical relevance of the topic, while a close commentary follows each paragraph and explains it as in Taber 2005? and so on).
6. Just as a personal aside, I would also recommend to agree about a realistic timing. I find it very frustrating to keep a dead line, notwithstanding all, and then have to wait for moths for the others to be ready with their part.

What am I forgetting? Is there something else one should agree about before starting a joint project?