Question: I don't know how to put it. I have never published before. Previously my one paper was rejected, that was because the experiments were not ready and my advisor asked me to still submit it just to have practice.

Now, 6 months later, I am writing another paper (on a similar topic). I have done some experiments, some are still going on. My advisor had advised me that "even if your experiments are not complete you should still start writing the paper". 

But I'm doing a lot of procrastination and I think I am scared of writing and possible rejection. I have done a lot of writing in other forms before, like blogging etc. But the thought of writing an academic paper with all the stringent rules (everything has to be clearly written, cited, nice flow of thoughts) is scary.

Please let me know how should one's mindset be while in the process of writing a paper.

Answer: 
This is not really a complete answer, but it's too long for a comment, so here goes... 

Remember that whatever you write now is not going be submitted. You don't need to overcome your fear quite yet because you're just putting words on the paper for your own sake. Just open your favorite text editor and write down everything you can think of. Forget about editing. You are just taking notes so that *you* can read it later and understand what you did and what you had on your mind. Don't filter yourself. You are just emptying your head to make room for new things. Write to forget.

Then, when you run out of things to write, go back and clean it up *a little* -- until you think of something else to write. Rinse and repeat.

As the content gradually becomes more complete, you will have more time and peace of mind to work on the quality of the writing and aligning it with all the best practices and advice and theory and rules of academic writing.

But for now, what's the first thing you think of that you've been working on in your project? Now open your text editor and write that thought down.
Like anything else in life, perform the task with the goal to succeed, and the likely outcome of failure.

Understand that rejection is all a part of the game. Very few people succeed more than they fail. As a matter of fact, upwards of 90% of all academic papers are rejected for one thing or another.

The most important thing is to keep track of mistakes that you've made with past academic papers. Write them down as bullet-points on a separate sheet of paper. Keep that paper right in front of you as you work on other academic papers to remind you of what **NOT** to do.

Practice makes perfect. If you're just starting out, it's likely that you're going to have many failures before you have a successful one.