What are your most common Calls from tenants?

I am new to this land lording thing... So, any insight you have is appreciated. What are the most frequent calls you get from your tenants and how do you respond? I want to anticipate how to handle tenant concerns. I want tenants to feel comfortable calling for legitimate problems, but I don't want to end up having high maintenance tenants. I think there are some things a tenant should be expected to resolve independently, however, I also want to be made aware if there's something that they cannot handle.