How to create a Very good admin user interface for the website backend system
Best way to start a 'very good admin user interface' is to start sketching using paper and pencil (sharpened).
You should spend some time with paper and pencil and figure out a few things:
1) Hierarchy: what stuff needs to comes off the main landing page and what stuff can be considered "second level" stuff. Some of this will be based on use; for instance, user stuff (account maintenance, user disk space, etc.) can probably all be grouped together into one tab. From that tab you can present individual user account options (maintenance, disk space, etc.) Other "Main tab" items you may want to include include stuff like System stats, Backup / scheduled tasks, database stuff, etc.
2) Keep it clean and simple. Don't go any more than 5 tabs on any page - if you feel like you have more than this many look at where you can either create a higher level page or combine stuff
3) Keep your pages simple, too. One topic to a page, and since it's an administration interface nothing should go below the fold.
4) No more than two or three sub-levels per tab. Your users won't want to have to burrow that far down, and it'll slow use of the interface. This is why pulling out the pencil and paper early is required.
5) Use common sense and standard design principles when it comes to the GUI. Use redundancy on any buttons (e.g. put the words "Release the hounds" under / on top of / next to the picture of the dog so non-native speakers can understand the button's use and non-graphical people can still read what the button does). Use the same button / graphical styles throughout, especially when it comes to commonly used buttons like "exit". You can color-code your sections but make sure that the colors are consistent (e.g., "green" is always system related pages and all system related paged are always green).