(This post is mainly for those junior students who are leading their research projects. If disagree, please read the disclaimer.)
When you disagree with anybody, no matter how stupid you think others’ ideas are, always express your opinions in a respectful way, because it is necessary to maintain a good team relationship and sometimes you are actually the one who is wrong. For example, instead of saying “I don’t believe it will work” or “I don’t want to do this”, it is much better to say “I’m afraid it will have some problems like …” or “I think it may be better to do …”. Also, don’t ignore any explicit question from your collaborators, regardless of how simple it may be to yourself. When they ask, it is a real question and they are seeking answers (or at least some thoughts) from you.
Start from the big picture.
When begin a discussion or a meeting, always try to start from the big picture, e.g., the high level goal of the ongoing test/experiment, before jump into technical details at the very beginning. Furthermore, when communicate with those who are busy with multiple tasks, it usually helps to remind of the context, such as the conclusions in the last meeting.
Provide reasons whenever possible.
I find it very useful to provide reasons together with the conclusions, especially for offline communication like emails. It will significantly reduce the chance of potential misunderstanding/confusion and thus improve the efficiency of the communication. Different people think about the same problem in different ways, even for those who have worked together for a long time. So it might be better not to take it for granted that your collaborators will understand your opinions.