It makes sense to approach a museum the way a seasoned traveler approaches visiting a city for the first time. Find out what is available to see. In the museum, find out what sort of exhibitions are currently housed in the museum and start with the exhibits that interest you. If there is a travelling exhibition, it "2019 always a good idea to see it while you have the chance. Then, if you have time, you can look at other things in the museum.
Make notes as you go through the museum and accept any handouts or pamphlets that the museum staff gives you. While you should not quote anything from the printed material when you do your report, the handouts may help to refresh your memory later.
The quality of your experience is not measured by the amount of time you spend in the galleries or the number of works of art that you actually see. The most rewarding experiences can come from finding one or two (1 or 2) pieces of art or exhibits which intrigue to you and then considering those works in leisurely contemplation. Most museums even have benches where you can sit and study a particular piece.
If you are having a difficult time deciding which pieces to write about, ask yourself these questions: (1) If the museum you are visiting suddenly caught fire, which two (2) pieces of art or exhibits would you most want to see saved from the fire? (2) Why would you choose those two (2) particular pieces?