Here are 3 ways to maintain consistency in your navigation:
1. Use global navigation (which is a set of your main links that appears on every page of your site in the same place).
Global navigation is an absolute necessity. It ensures that visitors can always get to the main sections of your website quickly and easily.
Global navigation options must be the same on every page. Many sites resoundingly fail in this area. Often, the order of the links varies from page to page, or some links are missing on certain pages. This confuses even experienced web users.
2. Keep the appearance and placement of buttons and secondary links the same throughout the site.
I recently ran across a site that used three completely different styles of buttons in as many pages. This variation blew any unified appearance they hoped to have. It also made it hard to recognize which graphics were links and which were not, since there was no consistently-used symbol for "clickability".
On another site, secondary navigation options were on the left on some pages and on the right on other pages. That's a no-no. Visitors will never be sure where to look for additional options, particularly since this site was visually busy. Don't move links around from page to page.
Link colors, button styles, fonts, and placement should be the same throughout the site. The goal should be for visitors to instantly recognize a link when they see it.
3. Stick with conventional design standards.
In addition to being consistent within your site, you also need to be consistent with other sites. Don't get too far out on the fringe in trying new things.
If you use a navigation scheme that's completely different from what you see on most other sites, visitors will likely be confused. Make your navigation look and function like something visitors will be familiar with from other sites.