Our goal here is to help the senior students and postdocs prepare for professional talks, departmental seminars and job seminars. The focus is on giving them the feedback that they need to improve. You don't do them any favors by telling them what you think they want to hear.
The talk may be informal, with questions blurted out in the middle, and may have funny stories. But formal or informal, it is worth looking for the following points. These points also apply to giving lectures, and many apply to writing papers.