Key principles to achieve a good interface with complex content... I am here going to assume more of an application than a standard company website (what, where, who, when).
First; as indirectly mentioned in a comment above; make things as simple as possible but not one bit simpler. The article In defence of hard has some really good points in that department. Do not dumb down, if it is complex then do not force it to be simple. Complex is good. Complex is interesting. Done well.
As an analogy: creating something - anything for 10 year-olds does not mean to boil things down to the lowest common denominator. 10 year-olds are used to that there are a lot of stuff they do not know and have to work out. This also goes for adults. Spoonfeeding simplicity is dumbing down both the user and the creator. Important things gets lost.
- First, I would say: use elements that are known to users in
general. To navigate space in some way, the principle elements of
Google maps and/or Google Earth is pretty much universally
understood. Plus, minus, zoom, move, overview etc .
- Also, the principles of computer games such as first-person adventure
should also be pretty clear.
- To navigate time, there are timelines galore. And to combine
time-space well can be very difficult but absolutely doable.
Using elements that most people are familiar with; there is no need to reinvent the wheel over and over. Most things have been done or attempted. Stand on the shoulders of giants, learn what complex interfaces fail and rethink the concept.
The art is to keep complexity, but not overwhelm the new user. Display the basics immediately, then increase options gently.
That, methinks, is the basic principles.