You can learn a lot by watching other people do things. You can also learn a TON from YouTube! Watch some videos, but be sure to check the comments too. Sometimes you'll see that the comments tell you the quality of the video and if they are showing you the right way. You'll find some really great contractors on there with lots of videos that you'll learn to trust. I always say that I'll try it myself and if I screw it up I'll hire someone else to fix it for me. I figure with all of the things I can do myself it has worked out okay so far. I do demo, tile, drywall, painting, flooring, lighting, shiplap, trim, etc. You learn as you go. The amount of money you will save will more than pay for your screw ups or the things you just don't wan to tackle. I recently flipped a house and hired out HVAC and electrical panel/wiring updates. I also hired someone to convert my stove from gas to propane because I just didn't feel comfortable doing it. I saved so much money that I was also able to hire a painter for some of the outside. It was 2 story Dutch Colonial with dormers and I just didn't feel comfortable with it. He did part of it and I did part of it and the garage. I still made $25,000 on the sale after closing costs, which is good since it's a small town. I paid $52,500 and sold for $125,000.
I also own an 8-plex. One thing to remember with rentals is that they aren't model homes. Don't overdo it! When I first bought it I remodeled 2 of the units. I spent way to much and completely overdid it. They are really nice, but the other units rent just as well. Definitely provide a nice, clean place for someone, but only do what is necessary for your market.
Start small and work your way up as you go. Don't buy something with so much work that it overwhelms you. Good luck!