I almost never get legitimate email in my spam folder and when I do it's a mass mailing (newsletter type of thing, usually with hardsell marketing).
In term of outgoing mail, if you are not sending from a email@example.com address, you need to make sure that you have set the SPF set up correctly. Lots of email providers have gotten more serious about checking in the past few years and if you are managing non-gmail.com addresses through gmail, your SPF settings will be wrong.
I formerly had gmail as a secondary account and recently switched to gmail using an address on my own domain because I was previously having such deliverability problems, both sending and receiving.
I'm not in the business of selling gmail though. I would in many ways prefer to be using anything else because of general uneasiness about gmail handling my email, but the simple fact is that they have a good job of it for me.
That said, I am afraid of the fact that I am at their mercy and they have no customer service number so if they decide to cut you off you are completely screwed. I don't have a great answer to that, but I do try to regularly pull all my email into Thunderbird so I have an offline backup somewhere.