Most common repairs to be made in multi-family houses

[Travis H.]

Quick version: In your collective landlording experiences, what would you say are the most consistent maintenance and repair issues that you run into, particularly when dealing with multifamily houses.

Backstory: I'm selling my house. Since this is kind of a new start for me, I've decided (after lurking a little bit on this site) to obtain my first multifamily property. (Also, is that a hyphenated word or just a regular compound word?) 

My finances aren't quite where I want them to be yet, though, so I'm going to wait until they are. In the interim, I want to practice some of the basic repair skills that I'll need to draw upon to be the sort of landlord who doesn't have to blow cash on a contractor every time the tiniest thing malfunctions. 

Thing is, I don't know where to start. So, I've come here to ask you: What are some repair and maintenance skills that I absolutely MUST learn to maximize my effectiveness as a landlord. I take book/YouTube recommendations, too!

Finally, do any of those skills require standing in order to practice? Weird question, I know. I have a broken leg with about three weeks left in the cast, but I'd still at least like to get started now with some of the easier tasks since I've got the time on my hands. 

Anyway, thanks very much for the assist. I'm planning on being much more active in this forum in the coming weeks. I joined a while back, but sort of went through an I-don't-know-what-to-do-with-my-life phase that seems to have come full circle. Is this what my thirties are going to be like?