Dashboard design is unique in it's challenges. Huge amounts of data need to be connected and displayed in a way that feels meaningful and intuitive to the user. Even the best data set in the world couldn't withstand the horror that is a useless presentation layer. Below are some key mini-lessons to review before launching any data visualisation feature within a webapp:

Be Meaningful

Ask "why" before you spit information back at a user. Charts and numbers do not necessarily equal insight. Every piece of information should be there for a reason, not just because you collected it.

Be Organised

Provide an overview screen or summary, with the option to drill-down into deeper insights. Not only does this help the user mentally process the data, but it supplies you with key analytics regarding your user's behaviours and interests.
For conversion flows, less clicks is always more, but this is often not so when when a user is logged in and engaged with a functional app. More page levels of hierarchy can often be better than scrolling endlessly through charts and displays.

Be Interesting

Use colours purposefully. Light to dark, bright vs muted, blues vs yellows - every colour should fit into an overall structure of visual cues.

Be pragmatic

There is no end to the supply of stunning dashboard mockups for inspiration, but charting is often expensive in development time. Choose wisely, focus on being informative, then add some unique elements where time and budget allow.