Looking for tips adjusting comps when determing ARV for a rental

[Michael Wintermyer]

I am in the beginning stages of learning about real estate investing and educating myself. One subject/topic that I am currently focusing on is analyzing a property--specifically rental properties. I have a basic understanding of ARV and how to calculate it but am looking for advise on adjusting comps to the subject property.

How can you determine the amount to increase or decrease for different features that differ from the subject property?

For example:

Lets say the subject property is for sale for $150,000 and has 3 beds/4 baths. A comp property sold for $160,000 and has 5 beds/4 baths. How do you calculate the amount to decrease from the comp property for the extra 2 bedrooms? 

This is just a simple example and other features can become even more difficult to determine so what are some of  the best ways to figure out the numbers in order to be as precise as possible?

Any advice is appreciated!

-Michael