RCTgo

I recommend looking at other players' styles and techniques, slowly imitating those you really like. Sounds like terrible advice, I know, but it's very helpful. Once you've copied from people enough, you'll be confident enough to stray off the beaten path and try more original concepts. Without that exposure to years worth of other people's work, you're pretty much left reinventing the wheel over and over.

The second thing has been said by Blazing here, just look at real life shots of whatever you're trying to capture. In addition to that, if you're willing to work that far, I highly recommend trying at least one full-on recreation of a real theme park. You'll gain tons of experience from noticing how the architecture, the foliage, the general park layout and all the rides were built in real life by trying to capture them in-game; can't do fiction without knowing how reality works.

[PS: 10 days late to the party, I hope this bump was worth it]