My husband and I love sailing and wanted our little one, George, to enjoy it as well, so we decided a Nautical-Themed Nursery would be a good fit for him.
We have Sail-themed fabrics, art, and details in the nursery, but it is not 'cheesy' as far as a theme goes in my opinion.
Since the space was small, I felt like too many colors would be hard to handle visually, so I went for an all-blue theme choosing various shades of blue so that it did not feel matchy-matchy.
I have a two year old, and I am so glad that I did not opt for a very baby-ish nursery for either of my children because the baby stage lasts very quickly. So that is my best advice for designing a nursery: do not make it too babyish.
Also, because you spend so much time in the nursery, you should make it cozy, cheery, and your own taste.