First, you need to decide for yourself whether or not you think Barack Obama is a good president. If you are unsure, then I would suggest doing some quick research on his beliefs and decisions as president. You can focus this research on political issues that you personally have strong feelings about (immigration, foreign policy, the economy, health care, etc.). You can Google search terms such as "Obama foreign policy" or "Obama health care" in order to find articles about his stance and his decisions. Try to avoid opinion pieces, as you would want to form your own opinion based on facts.
Based on your findings, you will decide either yes or no. If your opinion is yes, that is he is a good president, then you will write about his decisions in a positive way. Below is an example of how to frame an issue in a positive way:
"I believe that President Obama's decisions on health care in America have led to more accessibility to insurance for people with preexisting conditions."
If your opinion is no, that he is not a good president, then you will write about his decisions in a negative way. Below is an example of how to frame an issue in a negative way:
"I believe that President Obama's decisions on health care in America have led to higher insurance premiums for middle and upper-middle class families."
Because this question asks for your opinion, you can also share how his decisions may have impacted your life personally.