What’s my queries waiting for?

Blocking is a natural part of all RDBMS, not only SQL Server. However, very often the server is not able to continue processing because of other reasons such as waiting for disk IO, network IO or something else. Using this knowledge can be a key differentiator when analyzing a busy system and ease your work in finding the bottleneck.
There are several scripts out there, but this is the one I use:

SET arithabort OFF   SET arithignore ON   SET ansi_warnings OFF   DBCC sqlperf ('sys.dm_os_wait_stats', 'CLEAR') go WAITFOR DELAY '00:00:20' -- every 10 seconds    SELECT    CASE       WHEN wait_type LIKE 'LCK%' THEN 'Locks'       WHEN wait_type LIKE 'PAGEIO%' THEN 'Page I/O Latch'       WHEN wait_type LIKE 'PAGELATCH%' THEN 'Page Latch (non-I/O)'       WHEN wait_type LIKE 'LATCH%' THEN 'Latch (non-buffer)'       WHEN wait_type LIKE 'IO_COMPLETION' THEN 'I/O Completion'       WHEN wait_type LIKE 'ASYNC_NETWORK_IO' THEN 'Network I/O (client fetch)'       WHEN wait_type LIKE 'CLR_%' OR wait_type LIKE 'SQLCLR%' THEN 'SQLCLR'       WHEN wait_type IN ('RESOURCE_SEMAPHORE', 'SOS_RESERVEDMEMBLOCKLIST') THEN 'Memory'       WHEN wait_type LIKE 'RESOURCE_SEMAPHORE_%' OR wait_type = 'CMEMTHREAD' THEN 'Compilation'       WHEN wait_type LIKE 'MSQL_XP' THEN 'XProc'       WHEN wait_type LIKE 'WRITELOG' THEN 'Writelog'       WHEN wait_type LIKE 'CXPACKET' THEN 'Parallelism Synch'       WHEN wait_type IN ('WAITFOR', 'LAZYWRITER_SLEEP', 'SQLTRACE_BUFFER_FLUSH', 'EXCHANGE',          'REQUEST_FOR_DEADLOCK_SEARCH', 'KSOURCE_WAKEUP', 'BROKER_TRANSMITTER', 'BROKER_EVENTHANDLER', 'BROKER_RECEIVE_WAITFOR',          'BROKER_TASK_STOP', 'ONDEMAND_TASK_QUEUE', 'CHKPT', 'DBMIRROR_WORKER_QUEUE', 'DBMIRRORING_CMD',       'SLEEP_TASK', 'CLR_MANUAL_EVENT', 'CLR_AUTO_EVENT'       )       THEN 'IGNORABLE'       ELSE wait_type      END        ,waiting_tasks_count       ,wait_time_ms AS 'Total Waittime'       , wait_time_ms/waiting_tasks_count AS 'Average waits in ms'       ,max_wait_time_ms AS 'Maximum Waittime'       ,signal_wait_time_ms     FROM sys.dm_os_wait_stats   WHERE wait_type NOT IN ('WAITFOR', 'LAZYWRITER_SLEEP', 'SQLTRACE_BUFFER_FLUSH', 'EXCHANGE',          'REQUEST_FOR_DEADLOCK_SEARCH', 'KSOURCE_WAKEUP', 'BROKER_TRANSMITTER', 'BROKER_EVENTHANDLER', 'BROKER_RECEIVE_WAITFOR',          'BROKER_TASK_STOP', 'ONDEMAND_TASK_QUEUE', 'CHKPT', 'DBMIRROR_WORKER_QUEUE', 'DBMIRRORING_CMD',       'SLEEP_TASK', 'CLR_MANUAL_EVENT', 'CLR_AUTO_EVENT'       )   ORDER BY wait_time_ms DESC     SET arithabort ON   SET arithignore OFF   SET ansi_warnings ON