Some of the most important Counters regarding SQL Server Perf Tuning

Here are some most important counters:

Processor: %Processor Time
This counter should usually be less than 90 percent
System: Context Switches/Sec
On a multiprocessor computer, if this counter reaches 8000, and the Processor: % Processor Time counter is over 90 percent, consider enabling SQL Server fiber mode scheduling
System: Processor Queue Length
This counter should never be consistently greater than 2
Processor: %Privileged Time
This counter should be as low as possible
Processor: %User Time
This counter gives the percentage of time executing user processes such as SQL Server
Memory: Available Bytes
This counter should be greater than 5,000 KB
Memory: Pages/sec
This counter should never be consistently greater than zero
Process: Page Faults/sec
A high number indicates excessive paging
Process: Working Set
This counter should be greater than 5,000 KB
SQL Server: Buffer Manager: Buffer Cache Hit Ratio
This counter should be greater than 90 percent
SQL Server: Buffer Manager: Total Pages
A low number may indicate frequent disk I/O, more memory may be required
SQL Server: Memory Manager: Total Server Memory
If this counter is consistently close to the amount of physical memory,
more memory may be required
PhysicalDisk: %Disk Time
This counter should be consistently less than 90 percent
PhysicalDisk: Avg.Disk Queue Length
This counter should be no more than 2 times the number of spindles
PhysicalDisk: Disk Reads/sec
This counter should be consistently less than the capacity of your hard
disk subsystem
PhysicalDisk: Disk Writes/sec
This counter should be consistently less than the capacity of your hard
disk subsystem