You can get all the previous year papers from the official website of Banaras Hindu University only, by visiting the link provided below;
Going through this will help you understand the paper pattern, topics, and other relevant details related to preparation of the exam.
You can always get sample papers online at your ease. BHU UET is an exam which requires immense practice. Here is a link:
Moreover, you should also have a look at past year question papers.
This is the link for the same: http://bhuonline.in/old-qus-paper-entr.html
You can also get many books online of arihant, toppers.com, etc. Go for the one which suits you the most and try to stick to it.