This has been asked a lot around here, but I'll answer again.
Pro-tip: study hard, do well in your classes, get involved in extracurricular activities (i.e., things that show service and leadership), and stay in good shape. Nobody will care if you flew a Cessna prior to the Navy. They will care about your ASTB scores/GPA/leadership experience/etc. I have squadron mates who never touched an aircraft prior to the Navy, and others who had their ATP before the Navy, and a lot of variation in between. Guess what!? They're all Rhino pilots or WSOs now. Point is: if you want to work on flying before the Navy, that's great. Understand that the Navy wants applicants who are morally, academically, and physically well-rounded, and you may learn to do things in a private flight training program that's contrary to what the Navy teaches and will have to "un-learn" bad habits at some point in Navy flight training. We do things differently because we conduct training evolutions and operational missions that are far and away different than simply being an airline pilot both in complexity and in the skills required. Hope that helps. Best of luck to you.