What type of Improvements in a Rental to raise Rent?

[Chris Pierog]

I am working on getting a new rental in the makes. 

So far, these are the photos I have, they are older, and I am getting a walk through soon.

To give you a little bit of the background, this is in a decent location. 

Four-plex with 8 br and 4 bath, each having 2 br and 1 bath. Not in too bad of condition but definitely can be spruced up.

What would you improve in this rental to add value and  increase rent just from looking at the photos?

What are cheap and effective things to replace, fix, or add into rentals to add value and increase rent?

Any advice, experience, or tips  would be greatly appreciated :)

Have a good day!

-Chris