To identify the rate of change (or unit rate) I would usually look for a pattern in the table or graph. For example, if I got a problem like what is the unit rate for price per pound of potatoes and they gave me a chart like this:
Price. Potatoes
1. 3
2. 6
3. 9
I could determine that the unit rate (or rate of change) would be that for every $1 you could get 3 potatoes
I hope this helped! Have a wonderful day! :-)