Woah boy, I feel like I could list hundreds of things, but I'd say step one would be: All building descriptions written, and all icons in the top bar given a brief (emphasis on brief) sentence description of what it's for.
In past Arcen games, I felt help box descriptions tended to be too wordy, this game feels like the opposite extreme. I think it's OK to have a bit of wordiness in the right-click description box (to a point..), but I think we need a one-liner description in the tooltips for them as well. I think the 'at a glance' tooltip before you even select the buildings need a very brief "what it does" description there as well. If the main purpose is to give you 500 crops, then say +500 *crop icon* on it so I can see what it is for. I feel like I have to memorize every building before I can play the game comfortably at all.
The tooltip description at the bottom left shows more detail, but I think that can be cleaned up a little. Highlight what the build DOES more than other information about it. Rural farms give you crops. That should be the FIRST thing it says. Not the crown cost or how many turns. What it does should probably be separated a bit from the other details. Right now if I hover over farms, the fact it gives crops is the third line, it feels buried. Every building I feel like I'm hunting for the line that tells me what I actually care about. Max health? BANISH IT TO DETAILS WINDOW, BANISH IT! I'm placing a farm because I want crops, why do I care about how much health it has, it doesn't tell me what the building is for.
Add icons for things if you have them, like power consumption, social progress, etc - colors as well. The user should be able to grok everything they need about a building at a glance.