You can follow the below instructions on how to clean mussels easily at home before cooking.
Keep mussels in freshwater
After buying mussels from the market now keep the mussels in a bowl of fresh cold water for about 30 minutes.
It helps the mussels to breathe and extract excess salt and sand stored inside it's shells.
Discard any open mussels
After keeping mussels in water, make sure closely cross-check whether your mussels are dead or alive for cooking.
To check this you can either squeeze them a few times or knock them with another mussel after that if the open mussels do not slowly close.
Then it is a sign that your mussels are dead. It is safe if you discard them and try the same way with the other one.
Rinse and Scrub
Now using a firm brush to scrub the mussel's outer shell to remove any additional sand or barnacles.
Furthermore, rinse the mussels under cool running water and place them inside a container with a damp cloth or paper towel before cooking.
Remove the beards
If the mussels have beards, use a sharp knife or kitchen scissors to cut them off. This is the tough, stringy part that extends from the shell.
You know most of the mussels have a common thin, sticky membrane known as "beard", which is made of a lot of fibre that is attached to the mussel's shell.
To remove the beard from the mussels just hold the mussel in one hand, cover the other hand with a dry paper towel, grasp the beard between your thumb and forefinger and pull it downwards towards the hinged end of the mussel shell.
In this way, you can easily remove the beard from the mussel without killing them.