(All Opportunities Won / All Opportunity Closed) * 100
Image Source: How to Calculate Opportunity Win Rate, Brainshark
Add relevant fields to your report (ie Opportunity Name, Close Date, Owner, Amount, etc.)
Add relevant filters to your report (ie Opportunity Type)
Adjust the time frame to the period you want to see the win rate for based on Close Date
Create a Summary Report, grouping by 'Won'
Create a formula field named "Win Rate" (Grand Summary, WON:SUM/RowCount, see details in image)