For WAT you need to firstly kneed to know how to craft an article/essay. Start by writing small articles of 200-300 words and then increase the length further. read and work on your speend and handwriting. Start leaning new words for which can convey better meaning to your writing. And:

Time Yourself

Practice writing on different types of topics (and not only the kind you liked)

Try to present a balanced view on the topic

Structure your thoughts first, and don’t start writing the moment you get the sheet

Keep the language simple and don’t overuse jargons you don’t understand

Be Concise

Make sure you get your tenses right in the whole article

Write regularly!

For PI, You shall start by knowing oyurself as thye first question will be "Tell us about yourself'.

You shall prepare 3 writeups about you in 100 words, 200 words and 500 words respectively. The the 100 one you need to tell about your basic backgroud like your name, family background, education background, strenghts/weaknesses and goal. 

200 and 500 writepus will be elaborated versions of the same like about your strengts and weaknesses with examples and real life scenarios, goals and objectives in depth, why MBA/PGDM and why in the college you're aspiring. Make sure to and an answer where you want the next question to start. Like tell about your hobbies at the end or a specific hobby. Make sure to differentite between intrests, hobbies and extra curriculum. Listeing to songs cannot be a hobby but interest. Prepare well and be confident, Speak in slow speed for more clarity and use vocab. Dress well, wear a tie, shave or groom your beard, comb your hair well, wear poished shoes, and most important, dont be nervous and keep smiling.