Are there improvement guidlines

[Kevin Colwell]

I am currently in the process of closing on my first apt building and I have a question in terms of improving the units. Is there any certain guidelines that you follow in terms of getting your return back on your investment?
Hopefully this doesn't sound too odd but the reason I ask is because all of the units are roughly $200 a month below market value and the improvments that need to be done would be new windows in all of them. The optional things that could be done would be the appliances and possibly some new linolium in the kitchen/bathrooms. That being said if I made the improvements on just one unit and it takes me a year to pay for the cost via the additional rent money is that considered a good investment? I feel like this is an obvious yes but I was just looking for thoughts on if any of you landlords view improvements this way. Thanks for your time as always forum :D