what rental property owner should do

1. Paint all walls a color I can get anywhere and use on all properties in the same combos. Always keep enough for touchups as needed. 
2. Get all ACs to be the same and on maintenance plans with local AC plans. Pay for the filters and send email reminders to replace filters as needed. You can count if they've been changed or not and delegate as required. This is also a good test as to a good tenant or not! 
3. Use all the appliances and keep broken ones as parts donors. 
4. Upgrade all faucets, hardware, door knobs, add digital light switches via Wemo or the like, replace all bulbs to LED, replaced all light fixtures to modern ones, change all door locks to numeric keypad or bluetooth, add little touches like Ring Doorbells etc. This makes tenants feel good about where they're staying! They will pay more for these and it's easier to rent models with them! I promise you this is a FACT.
5. Add quarterly maintenance. This allows me to survey the props, see if I want to rent to that tenant again a year later, let them know what needs to be improved upon as far as animal control, pest issues due to food left out, appliances cleaned to maintain some sort of self respect and cleanliness, etc. They actually like it, oddly. I like it too...it's easy to sell as a way to not lose their deposit money. :)
6. Trim plants, paint stuff and clean odd items quarterly really helps to transition from old renter to new one once the old ones move out. It's also faster to show if the place is kept clean. I assure you, nothing makes more money than a clean place! Nothing.
7. Don't accept late payments without a penalty. If in year one, don't accept without throwing them out after 1st year. If older tenants, work with them if you like them and you believe them to be mostly stable. Things happen but don't be stupid. No more than one per year max. with a penalty, no less. No breaks. 
8. Raise rent only if your costs really increase. If your taxes don't go up, don't charge them more. Why? We are all in this together and it's a symbiotic relationship. We need good tenants as much as they need good, fair landlords. Keep things on the up and up and be honest! That is what you'll get back in most cases. 
9. Change out carpets and replace tiles/flooring as needed. Replace with cost effective options and if you know how to do so, do it yourself. On years where carpets are replaced (every 5 without damage or animal issues) increase rent by $50 a month or so to make that cost up that year. 
10. Always have something new added every year. They notice these things and will want to stay where a landlord is doing their part.