For the most part, I only write about things I have firsthand knowledge about.
Since I've spent the last decade+ as a tax accountant and business consultant, I can honestly talk about topics like taxes, entrepreneurship, debt, credit, etc. with little hesitation.
In addition, as a homeowner I can discuss all areas of real estate from investing to owning without sounding like a complete rip-off of someone else since I have both the professional experience and personal homeowner stories to share.
Aside from that, I'll pretty much discuss anything that I feel is relevant or anything I have an opinion on (which is almost everything).