What design principles can be used to achieve simplicity without diminishing the ability of the user to use an interface efficiently for complex tasks?
Specifically, I'm wondering which key design principles I can use to achieve more with less. Principles that allow a designer to cover complex interface features with simplified, minimalist, design.
Having minimal buttons is the signature of a clean and simple interface. Find your top few interactions and give them buttons so they can be 1-click operations.
If those interactions have advanced features, give them a toggle/dropdown/submenu of some sort, ideally 2-click operations.
Anything you expect your users to rarely click can be deeper in the interaction. You don't want 100 operations as the level/submenu as it will become cluttered. Based on your overall complexity, stagger your levels to keep a balance of levels/submenus vs overcrowding each one.
Try and keep everything but the rarest of interactions within 3-clicks if possible. Your groupings of functions may help you decide where they should go. Always group similar actions and try and combine functionality when possible (ie: a toggle switch instead of both an on and off switch)
Take a look at a few sites and count the clicks to the tasks you typically do. A well designed site will take typical user interactions into account. Everything you'd typically interact with should be in an intuitive location without looking cluttered.
To make your application easy to understand, use common elements and symbols that people are familiar with, rather than making them learn new symbols. Organize the system so that it walks the user through a process (e.g. step 1 should clearly navigate to step 2). Keep your navigation consistent (e.g. always keep your "save to draft" and "submit" buttons in the same order). If you have a dashboard or home screen, organize it well so that similar processes are grouped together.
The book, Don't Make Me Think, has great advice. Another good book is Neuro Web Design: What Makes Them Click?.
You ask how?
For many people there are many different ways.
This is what I do:
Write down the functions of your application.
Then start putting the functions into "categories", for example:
functions: chat, add friends, ignore list, play video. I can put "chat", "add friends" and "ignore list" into the same category, because they are related.
After this you can create a wireframes, a simple block version of your app and you can put your categories in.
Then just have fun with the graphic design.
For a complex application I would keep the graphic design open and simple. Maybe with the user of colors for each category, or simple icons. You need to make it look as if it is very easy.
I hope this answer helps you.
As I've said earlier in this answer, everyone has his own way of making an overview of their project.
Good luck.
I need to design an interface that clients don't have to spend more than a few minutes learning to use, but still offer advanced control of the the features that the application offers.
These, I would argue, are unrealistic requirements. At least, they are unrealistic until some user research is performed.
So that's where I'd start. The design principle I'd go with is user-centered-design.
Upon researching the needs and habits of the users, however, we may very well come to the conclusion that the tasks simply are complex, and that trying to force them into a 'simple' UI may actually be a detriment to the user. To figure that out, I'd use A/B testing.
In summary, I'd leverage User Experience testing and research principles first and foremost.
Focus on meaning. Here are some thoughts:
To make something meaningful, you need to profile your target user: What does she know about this new task? Are there similar tasks (perhaps from other domains) that can acts as metaphors or illustration?
Simplicity should be the result of making things meaningful. Don't focus on simplicity. Simplicity can hide the real thing and make things harder to understand: less meaningful.
Be forgiving, and allow users freedom to play and do things in different ways. This is much more work to implement, but will make users happy because it gives control.
Keep a good eye on locus of attention. We humans are easily distracted and focus on one thing at a time. It's therefore making things meaningful if an interface takes this into account.
Read books, and learn about human nature, psychology, ergonomics, ... Interesting company is IDEO.
It's a staccato answer, but I hope it sets you off. Good luck.
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.
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.
