What is the best approach in learning UNITY3D?

I am a mere beginner in games development , but I do have some basic knowledge of 2D games development. What is the best approach in learning UNITY3D? I mean any good books ? Or some online tutorials? What’s the best way to go?

NOTE: My preferred platform is Android OS.

There is a Teaching subforum specifically for you.
http://forum.unity3d.com/forums/23-Teaching

Other than that, this topic has been discussed a lot already, and there are lots of articles out there just waiting for you to google!

Personally I enjoy Video Tutorials, of which you can find many at YouTube, or something like Udemy, Lynda.com, or Digital Tutors.

The “Best Approach” is different for everyone. I respond well to videos, other people prefer more text-based tutorials. Some prefer to just dive right into it and try to figure out everything themselves using nothing more than Unity official manual. Bottom line is you need to figure this out which approach is best for yourself

I like to learn some existing projects and then work around with my own. Are there any video tutorials for some existing 3D games? There are plenty out there , but for a beginner its really difficult to figure out the best out of those.

If you like to learn along a project, then have a look at these tutorials from the Unity guys: Link

For each project you can download the assets, which come along with a set of video tutorials that lead you step by step through the project.

There are lots. I have already stated in my previous response where you will be able to find them.

If you really want someone to tell you which one you should watch, then maybe try this one:
https://www.udemy.com/unity3d-concepts/?sl=E0IbczFTKn1uFFkoCkA%3D&dtcode=mf9zjcjn

I have not watched these myself, but it is Free, and the topics it covers at least seem good. Give it a go.

Dive in and plow.

Yes. Doing is the best approach for learning. Pick a small project and try to solve it.

I agree with the just doing things, the best things i’ve learnt have been from getting stuck in

I will say though that a great resource for interesting articles and tutorials is http://unitygems.com/

Some real eye opening things in there