Salesforce.com report is a simple, yet very powerful feature. Out-of-the-box, it come with multiple type of reports, and admin can create more custom report type as needed. With report builder introduce few years back, it even easier to use and more user friendly.
But, sometimes you may found that report take sometimes to load, or time-out (although this is very rare happened).
What is the caused?
1. Too many columns in report
Just add columns as needed. More columns to display will take more time to run report. You also can hide details, when it needed, just click "Show Details" button.
2. Too many records
Set report filter criteria correctly and efficiently, you can add multiple criterias and time frame.
3. Inefficient filters
Contain and Does Not Contain take longer time to load report.
Report using AND will load faster than OR.
If you have tune everything above and it still slow, you can schedule report for future run and email it to you daily or weekly.
For more information, watch this YouTube video.