Our team is called upon to review other people's applications and give them feedback to help them improve. We usually give a presentation about UX design first then we look at their app. It is easier to give advice on poorly designed apps than advice on apps that are mostly correct. The reason is that broad, generalized pieces of UX advice solve most of the bigger problems. These ideas aren't original but they can be relied upon to work again and again for most design problems. They will get you most of the way there.
The hard part is in the last push, to take an app from OK to great. This is where you need originality because the particularly unique problem that you are solving calls for a particularly unique design idea. A bespoke design solution requires listening to the unique requirements of a project and creating something new from existing materials. Because you are forging ahead into unknown territories, it involves a lot of trial and error. The way off the beaten path of generalized advice requires bushwhacking your way through the tangled mess of the unknown, knowing that sometimes you will have to head back and try a different way. The reward however, for breaking through to something new, is worth the effort.