What are the different ways to get backlinks?

I used to do marketing through different SEO techniques and my competitive site also was started on nearly the time i started website.

But when i checked their backlinks it is increasing to lakhs and millions very very fast…how?
Any method i can find how they are doing so fast and improving rank with not very heavy content?
A bit confused.

I have been in the market of SEO for 4 years from now and have seen and implemented a lot of link building techniques. I will suggest you not to follow your competition in number of growing backlinks as they will see a quick boost in the rankings for a small amount of and after a few months a google algo update will roll out against these spammy links and they will get penalized. Just go with your flow and be consistent in making quality backlinks. Backlinks are about quality not quantity. A relevant backlink from an authority site is far better than random 1000 blog comments. Some companies hire agencies to do this shitty work for them and they don’t even know how agencies are manipulating them by ranking for a short amount of time.