I have taken jeemains exam two times .Can I take jee advance(2018)? Sir I got 68.8% in 12 class from up board(2016).Please reply.

Ashif,
The Ministry of Human Resource Development, Government of India has notified following two changes in the JEE pattern for 2017:
1.There shall be no weightage for the 12th class marks in calculating the ranks in the JEE (Main) examination,
2.For the candidates to qualify for the admission in the IITs/NITs/IIITs and such other CFTIs whose admissions are based on the JEE (Advanced)/JEE(Main) ranks, they should have secured at least 75% marks in the 12th class examination, or be in the top 20 percentile in the 12th class examination conducted by the respective Boards. For SC/ST students the qualifying marks would be 65% in the 12th class examination.
Now, according to this you can not participate in JEE counselling so, better option is to try for admission on the basis of what you have scored this year.
You can try with these marks in some good private universities like Lovely Professional University, Jaypee University, Manavrachna University, etc where the admission criteria is your marks in class 12, JEE marks or their own tests. Most of these universities have good infrastructure, learned faculty and good placements. The environment is conducive to learning and growth. Some even offer scholarships to meritorious students.
Best of luck.