The advanced search (and the reports) is one of the most underestimated and underused feature. Organizing tasks in projects is one thing, building searches (and save them as reports) is another. With reports, you give even more value to your data. You can do your work more efficiently. You can detect issues earlier.
Here are the best reports I could think of, helped by the community! Don’t hesitate to submit your own using the comments.
1. All subtasks in given projects by @Bastien_Siebman
Subtasks are not always easy to see from the main list
Add filter > More > Subtask > Subtasks only
In projects
Completion > Incomplete
2. Overdue milestones by @Bastien_Siebman
Milestones are important to measure progress, especially in Portfolio and Timeline
Add filter > More > Milestone > Milestones only
Due Date > Within the last > 1 day
Completion > Incomplete
Also shows today’s milestones
3. Overdue tasks by @Bastien_Siebman
To avoid the overwhelming feeling and make sure the account stays clean
Due Date > Within the last > 1 day
Completion > Incomplete
Also shows today’s tasks
4. Incomplete project status update by @LEGGO
To find any status update reminder that was not completed
Search terms “Please update the status of”
Completion > Incomplete
5. Tasks without a project by @LEGGO
If your policy is to always attach tasks to a project
In projects > No project
Completion > Incomplete
Add filter > More > Subtask > No subtasks
6. Incomplete tasks without a comment by @LEGGO
Those tasks might be list
Completion > Incomplete
Add filter > More > People > Commented on by > Nobody
7. Incomplete and overdue high priorities by @Bastien_Siebman
Those are the tasks you should focus on first
Completion > Incomplete
Add filter > More > Custom Fields > Priority has value High
Due Date > Within the last > 1 day
Also shows today’s tasks
8. Last week team’s work by @Bastien_Siebman
To have an overview of what your team worked on
Add filter > Date > Completion date > Last week
Assigned to > team member
9. Manager delegation “volume” by @Bastien_Siebman
To have a sense of how much a manager is delegating
Add filter > People > Assigned By > Manager
Add filter > Date > Creation Date > Within
10. Overdue but blocked tasks by @Bastien_Siebman
Actually, those are the tasks you should focus on first 
Add filter > More > Dependencies > Blocked
Due Date > Within the last > 1 day
Also shows today’s tasks
11. Laser focus tasks by @TylerNow
What you should focus on when overwhelmed.
Assigned to > You
Completion > Incomplete
Due Date > Within the next > 14 days
Add filter > Add custom field > Approval stage > Is not > Ready for Review
Add filter > More > Dependencies > Not blocked
You can also filter on “Not waiting on client” if you have such a custom field
Any suggestion for more?!
