Posting your channel page in comments in Groups or as posts in any group of fb, Whatsapp etc helps. Apart from this you can also promote it by creating a seperate page on fb where you can link it to your channel by your posts. For adding more viewers & subscribers just reply to the comments regularly/periodically, this will enhance your reputation.

First you have to see what your channel offers and what is the target audience or people it might interest.

Making a separate FB page of your channel and sharing it with various groups on social media like WhatsApp will promote it. 

Promote it more among the target audience.

Have a good FB page giving detailed information in a interesting and user friendly way.

Above all stick to the quality of the work. It is your work that will count and the promotion will spread from mouth to mouth

Arunima Singh wrote:

First you have to see what your channel offers and what is the target audience or people it might interest.

Making a separate FB page of your channel and sharing it with various groups on social media like WhatsApp will promote it. 

Promote it more among the target audience.

Have a good FB page giving detailed information in a interesting and user friendly way.

Above all stick to the quality of the work. It is your work that will count and the promotion will spread from mouth to mouth

Apart for all above what Arunima said, You have to select Hot topics where you will get more audience regularly. Also, you can promote your Channel by approaching proper advertisement agents.