Home appraisal question?

Not sure what it might be called but I want to do a mock home appraisal for myself just to see what renovations I can do to improve the value of my home or what I need to work on. Also, I want to make sure I know what the home is worth before I put a price tag on it. My Realtor suggested 10,000 lower than I expected and I am positive this is wrong. How can I find the value myself, like a comparative market ysis maybe but I need a guide.