Your ignorance is really showing with this one. Keep them short and simple. Make sure they tell the visitor where he is. Don't use them unless they have a specific purpose. Poor Quality Graphics.
Nothing makes a site look more amateurish than fuzzy, jagged graphics.
If you are not into graphics, consider having someone else do them for you. Especially should your company logo and product pictures look sharp. No permanent cure for this little creature has been forth coming so one must be vigilant to check often. Broken links reflect a lack of maintenance. The link should be operable or it should be removed.