Hi Vidyarthi,
Welcome to 5 Star and thanks for writing a great 1st post that asks a great question!
Here are my thoughts and 2 reasons that back them up.
1) Your time/focus 2) conversion facts.
While I don't think there is any magic number or formula for when to add ads I do feel you need to focus on content 1st, then marking and building traffic to a certain level and then think about monetization.
1) Your time/focus - As soon as you start thinking about ads a whole new world of learning, problems, issues come up that takes you away from building your foundation (content/traffic).
We each only have a limited amount of time, so doing things
in the right sequence IMHO will help you get further faster.
Think of it like building a house. You've never done any of it before so you have to
learn how to pour concrete (foundation), frame, electrical, plumbing, etc.
Each stage takes time to learn PLUS time to complete (build that part of the house).
So if you get 1/2 the foundation poured and one side of the house framed THEN divert your efforts to start learning roofing and invest time and energy at that stage buying shingles and putting them up - now you're taking time away from finishing the foundation and framing you MUST DO before you can even start to think about the roof!
2) Conversion facts - Some affiliate programs convert
at only 1 sale out of 100 visitors. And that's AFTER you figure out how to pick
the best merchant, ad placement, presell and other things that can affect conversions.
It could take 1,000 visitors (random #) to make that 1st sale if you don't know what you are doing. Those 1st 1,000 could be turned off if they see a bunch of ads and no content. On the other hand if you have GREAT content, they could become regulars and tell their friends.
I think you'll lose very little in revenue if you build 1st, monetize later
and I think you stand to gain more in the long run.
So build a solid foundation before you worry about the roof! 
Make sense???
ONE CAVEAT - or just a contradicting thought I guess... I think it's really important for new affiliates to make that 1st sale as quickly as possible, so they get some positive re-enforcement and don't give up. So what I said above almost seems like it could delay the time of that 1st sale. I still think you'll earn more in the long run though if you build a solid foundation 1st. You don't have to work on it forever, just get a good base built before you worry about ads.
Note: this advice is only for n00bs. People that know how to build fast, generate traffic and run ads, can do everything in whatever order they choose.