As your income grows and you make sales always upgrade your wardrobe.

A few things it really depends on you and the property,  First off as many have already said screening is crucial if they can't afford the apartment paying for it will be difficult, second point to this is what kind of upgrades you do it is very easy to over upgrade in these neighborhoods and than want to squeeze every penny out of the rent, which will make it hard to find tenants that fit the 3x rent rule.

Check the roof, plumbing, electrical, heating, AC, pool, kitchen upgrades and bathroom upgrades because these tend to be the biggest expenses.

Keep in mind I manage this on behalf of another owner so I have to be conscious of their repair costs.  

BF marketplace requires upgrade. 

I think a little lipstick upgrade would go a long way on this one.

Im in process of upgrading all of my hot water heaters in my 16 unit apartment complex.

I read somewhere that back in June (when my trouble started) that they upgraded their pricing algorithm and now Zillow could essentially 'read' your pictures to tell how updated and modern your home was, if it had granite countertops or formica etc. 

I upgraded the entire property (inside) modern finishes sell!!

My brother and I bought a SFR recently and were curious what you have found is the best ROI for upgrades in the Denver area?