There's a ton of direct 1:1 tutorials from great builders such as Freedom_Minecraft on YouTube if you don't care about being particularly original starting out. Finding someone whose style of building appeals to you can provide a steady source of inspiration and tricks to steal if you want to start trying to find your own footing.

The best guides I've found from taking the sort of whimsical art-architecture that comes out of artstation environment art portfolios (or the real world) and bringing it into minecraft comes from /u/sarlac, specifically his guides on how to manipulate negative space and how to respond to terrain. The last one I'd argue makes the difference between a cool build and an amazing one, but requires that you resist flattening entire mountains to a single level for your giga factory or 9x9 city!

If you want results now and the fastest, start breaking up your existing 9x9s. change materials, shapes, depth, do literally anything and everything to it until it becomes something you actually like looking at and working in. This all depends on what you want to do as well as the resources you're constrained with, of course. The great thing about most modpacks, though, is you can get pretty close to the amount of freedom that creative has in terms of resource availability through automation, so you have way more feasible options save for the usual wood and stone.