You gather or identify the data sources first.
Analyse the KPIs from it. Decide which chart or objects will be best to show the KPIs chosen.
Do necessary alignments and formatting wherever needed.
Finally go for the optimization.
You can go through some sample demos here Qlik Demos: See QlikView in Action | Demo.Qlik.Com
to get some understanding on how the dashboards are built.
Also find the attachment to get the base to build the dashboards.