Learn to how analyze and critique scientific papers. Writing reviews will enhance the knowledge about state-of-the-art works and will teach how to evalaute and critically analyze the works.
Brief summary
What is the problem the paper is trying to solve? What are the key ideas of the paper? Key insights? What is the key contribution to literature at the time it was written? What are the most important things you take out from it?
Strengths (most important ones)
Does the paper solve the problem well?
Weaknesses (most important ones)
This is where you should think critically. Every paper/idea has a weakness. This does not mean the paper is necessarily bad. It means that there is some room for improvement and future research can accomplish that.
Detailed Comments
Can you do (much) better? Present your thoughts/ideas.
What have you learned/enjoyed/disliked in the paper? Why? In which situations the approach will work or will not work? Can you use this approach in your research? What future research directions should be explored?