Visitor Visa - B2

Hi Readers!

I would just like to ask some opinion/suggestion coz i am planning to re apply Visit Visa this January.
I got rejected last April 2018.

I am Single, 25 years old, and I have relatives IN USA In which i declare on my previous application.

Questions that time are...

What is the purpose of your travel?

I would lovw to visit New York and visit my Grandparents.

Are your grandparents american citizen?

Yes, they are US citizens

How they acquired their citizenship?

Im not sure how they acquired it(honestly i dont know)

What is your work?

Im an HR Asst. In xxxxx

How long have you been working there?

More than 3 yrs

Have u traveled before?

I went to italy last yr.

Are u married?

No. Im Single

After typing.. He handex me a white paper... Rejected huhuhu

VO: i cannot give u right now coz you dont have a clear purpose.

Me: thank you, Sir

He did not ask for fir any documents.. Please advice me.. The do's and don'ts..

Thanks in advance!