This chart will give you a quick at-a-glace count of Cards that are currently active on your Board at any given time displayed Label or custom drop-down field. This chart is good for seeing how much work is currently allocated across different categories (ie. projects, stages of work flow etc.). You would want to create a separate one of these for each category or dropdown you would like to track.
This chart assumes you are using Labels or the dropdown field from Custom Fields (which is available with most Trello paid accounts - details here) to hold this data.
To get started, create a Count of Cards for open Cards.
A chart to see how much work you currently have in progress by Member.
A count of cards that have passed their SLA time frame for movement through your workflow.