In your case, you need to highlight the content for most users. The navigation bar should then highlight the sections dedicated to them.
For users who need to enter content instead, you can place an access/registered link above the main navigation bar and the same link in the footer. On the Home Page and other pages you could insert a CTA box (experimenting with different positions and sizes, especially if the ad placement will be your source of income.
This is just a generic idea anyway. There may be several other options. The important thing is to continuously experiment and analyze all data in the long run.