1) Buy the landlord tenant guide from NOLO press for your state. They are a legal press that provides contract templates and great coverage of the laws you need to follow and if you only read one book it should be this one IMHO. It provides a legal overview of all the rules (but depending on your city you may have additional research to do). I prefer the physical copy for skim reading. Many libraries actually have this.
2) Buy the NOLO press guide for landlord tax deductions--read it and then hire an accountant to help you deal with the tax implications (which can be super advantageous but need to be done correctly (along with depreciation). I always did my own taxes before (and they were super complicated with W2, two types of 1099 income, tuition income etc) but for liability reasons in case of an audit and in order to maximize your deductions and advantages I don't recommend landlords handle it themselves. I pay about $400 a year for this in a high cost of living area and think it's been worth it for me.
3) Figure out your screening process. Absolutely you want to run credit check and background check on everyone. I personally require high credit and three times income for the rent and use applications to only prescreen people I think will qualify then have them pay for and run the background check through mysmartmoves.com (though some states have started restricting the cost for background/application/credit checks so make sure the cost complies). I always call references--you would be amazed the crazy shit people will tell you.
4) I add a few additional restrictions to my leases--they must maintain utility service continuously (to avoid someone not paying a water or electric bill, getting shut off and thus violating habitability requirements), have to register all vehicles on the property to avoid abandoned vehicles, and everyone over 18 on the lease and do a background credit check no exceptions. I also ban smoking anywhere on the property and am very strict about this.
5) Do not rent to friends. Just don't. The only time I had a tenant break a lease earlier it was a friend. You will probably ignore this advice (everyone has to make this mistake themselves) but I say it out of caution so when you do it and it goes badly you can at least have some extra savings and your spider senses up to cover you.
6) Plan on vacancies. I didn't get our back unit on our duplex rented until we had been living in the property for six months. It took time to get ourselves moved in, settled, clean things up and get our process dialed in. In the time you aren't in the unit SHUT OFF THE WATER AT THE VALVE! That way if your old water heater fails (like ours did when no one was living in it) it won't leak everywhere.
7) Read read read about advice on tenant screening, experiences land lording etc. Bigger Pockets as was already mentioned is great for this.
8) Have money set aside to cover unexpected expenses. Get three quotes for all work. Wait to do any remodeling until you have lived in the unit. Don't go crazy over improving but definitely keep things up and plan to spend money between tenants.
9) Have consistent rules and communicate expectations up front, and address any problems (like tenants parking in the wrong place or storing items where they shouldn't immediately upon move in and don't let it go to avoid conflict).
10) If all your showings and prospective tenants just seem off pull it off the market and wait. We got stuck listing in March one year which is off cycle for our market and the people who came by were just not qualified, totally nutty, or clearly couldn't read and follow the listing. We yanked it, hosted some international students for a few months then listed in the summer and got great tenants.
11) Even if you are handy have 2-3 plumbers, electricians, handymen you like and trust already identified so you can fix issues within 24 hours. We've had the only toilet in a unit go out, or a water heater fail and sometimes even if you can fix it yourself if you aren't available you just need to get it fixed quickly.
12) Find a good move out cleaning company. In my market it took me calling through 15 companies to find someone I trusted that is affordable and does a great job. I only use them now, but you don't want to leave this for the last minute if you have someone moving in on a deadline.
Overall, our duplex has been a great investment, and we have been really lucky by sticking to strict tenant screening, making improvements over time, and handling the property management ourselves.