Help identifying key formulas

[Sammie Renna]

Hello All, I'm new to BP and was wondering if someone can help me with identifying key formulas to consider when evaluating a property as an investment, and also what a good percentage to be at? I currently own 2 condos which I purchased 10 yrs ago right before the housing market tanked. I was young when I bought these properties and didn't do any du diligence before purchasing them, I want to make sure I did the opposite this time around! I just downloaded the Ultimate beginners guide to RE investing by BP yesterday, which I plan to begin reading tonight. Thanks!