@Chanelle Dupre welcome aboard neighbor!
Cash FLOW is king as @Bill pointed out and many investors claim to understand that but yet don't know how much actually it costs to operate a property. Not just investors, but people who should know better too (cough Zillow cough) when they present cost of ownership ratios that seriously understate the cost of operating a property. See http://ashworthpartners.com/the-buy-vs-rent-meme-t... for more on that.
Many small investors (like many owners of small businesses) do not know their numbers well enough to even know if they're really making the returns they targeted because they run a lot of expenses out of pocket and ignore the value of their time. This is great if you're goal is bragging at the country club but if you're trying to build up or preserve wealth it pays to know your real numbers.
To do that imagine that you are the CEO of a large real estate company (or a singer/songwriter out on tour ;) and that someone has to paid a market competitive amount to perform every task associated with operating a property successfully on a long term basis. That includes managing the property, maintaining it and setting funds aside for replacing the big components when they inevitably wear out. Then add in the secondary costs, managing the managers, legal, accounting, etc. This is your true cost of operating the property and when you deduct these and the debt service from the actual Gross Operating Income you will know what the cash flow before tax is. Deduct for taxes and this is the true cash flow in your pocket.
Once you know the true cash flow, and presuming it is positive, you can decide how much it's worth to you as an investment. Cash on Cash Return is the first measure, cash flow in your pocket divided by your total investment in the property. It ignores the loan balance being paid down by the tenants and any appreciation that comes along but if the property isn't cash flowing enough you won't (or won't be able to) hang on to it long enough to enjoy those benefits.
The other measures such as IRR, DCF and NPV require that you correctly identify the selling price somewhere out in the future. The future is hard to predict as it has been said and so running these measure amounts to a guess at best. On the other hand if you can predict the future, I'd like to partner with you!
Good hunting-