@mpasanthosh Superbly explained Santosh.
Biasing is more critical to tube than SS amps. With SS amps, the variation comes mainly with aging components.
The procedure however varies from one amp to amp, and unless mentioned specifically in the user/service manual, technical help must be sought.
I have biased quite a few amps successfully based on information available either in the manual or from information obtained on the internet.
I have had bad experiences as well. I blew a of vintage JVC amplifier where one channel was a bit too off from the listed rating.
I just blindly followed the procedure listed in the manual, with the effort ending up in smoke.
Yes, if you get an used amp in hand and see the bias a little too off, it is better to check first for failing components around it.
Another issue I have observed is when some component associated with biasing is failing, even after adjustments it keeps falling off.
This too needs technical intervention.
Coming to the OP's topic of procedure involved, there are usually two methods, biasing the current or the voltage. Biasing the current is a bit more tricky as you need to put a multimeter (with current measuring feature) in series to the amp.
Another equally important factor is adjusting the DC offset which is measured between the speaker terminals in idle state.
Some amps provide for fine tuning this setting as well.
Here is an example as listed in the manual of Pioneer GM-X944
"ADJUSTMENT -
Setting Idle Current
Setting the idle current to the following ranges will require you to measure the voltage across the indicated resistors and adjusting the indicated variable resistors to set the required voltage range.
This adjustment is performed with no loads on the outputs with no signal input.
Specification: 45 mA ± 5mA
Voltage Range: 4.0 mV to 5.0 mV
1. Measure voltage across Resistor R433 and set VR501 to Voltage Range.
2. Measure voltage across Resistor R434 and set VR502 to Voltage Range.
3. Measure voltage across Resistor R435 and set VR503 to Voltage Range.
4. Measure voltage across Resistor R436 and set VR504 to Voltage Range.
Notes: The Idle current should be set when the amplifier has not been run for awhile, and set at room temperature. "