In order to write a review of a concert, here are some questions that might help you to organize your ideas:
What is the behavior of the audience? This will vary greatly depending on the venue and the type of music you are reviewing. For instance, are they sitting quietly, or dancing and singing? If so, how intense is their movement, and how does it relate to the music?
What is the affect of the musician(s)? How concentrated on their instruments do they seem to be? Do they have a score in front of them? How often do they look at it? How do they interact with the audience?
Is there amplification in use? Are the sounds processed in any way?
What can you say about the visual dimension of the concert? Do the musicians move around the stage or remain in one place? Is there video involved?
From the answers to those questions, what can you infer about the performer’s expressive aims? Is music the most important element of the concert? Does it share the attention of the audience with more overtly theatrical elements?
The structure of the music will depend very much on whether you are reviewing a classical, jazz or rock concert. Multi-movement compositions (symphonies, concerti, etc.) differ greatly from the concert presentation of a jazz standard, which has extended improvised sections, and both are different from a song (whether the song’s genre is pop, rock, metal, or country).
If the concert as an event consists of a sequence of songs, what can you tell about the playlist? Is there a global expressive arch, or are there peaks and valleys?
If you attend a classical concert instead, are the works by a single composer or by several? Do all the works belong to the same period and/or style?
What does the music seem to prioritize (pitch, rhythm, texture, something else)? Considering what you’ve learned in the lectures so far, what technical information can you provide your reader about the music you heard at the concert?
These questions are merely presented because they MIGHT be useful; obviously that doesn’t mean that your review should consist in a series of responses to them. This is a loose guide, not a questionnaire.