Yes, you are eligible to write JEE Main in 2018.

Below is the eligibility criteria of the exam you can check-

-Students who are born on or after October 1, 1993 are eligible to apply for JEE Main 2018.

-Candidates belonging to Scheduled Caste (SC), Scheduled Tribe (ST) and Persons with Disabilities (PwD), must have been born on or after October 1, 1988 to be eligible for JEE Main. Candidates of these categories have been given a relaxation of 5 years.

-Candidates must have passed 12thclass or qualifying exam in 2016 or 2017

-Candidates who are appearing in class 12thor qualifying exam in 2018 can also apply for JEE Main 2018.

-It is mandatory for candidates to have taken 5 subjects in 12thor qualifying exam

The 5 subjects for B.Tech/ B.E. are:

1-Language, 2-Physics, 3-Mathematics, 4-Any one of (Chemistry, Biology, Biotechnology, Technical Vocational Subject), 5-Any other subject.

-For admissions to NITs/ IIITs/ GFTIs, candidates should have secured at least 75% marks in class 12th exam or be in the top 20 percentile in the class 12th exam conducted by the respective boards.

-A JEE Main candidate can avail 3 attempts for the national level undergraduate engineering entrance exam.

You can also check the eligibility criteria from the given below link

JEE Main Eligibility Criteria

Good Luck!!

Yes, you are eligible as 12th appearing students can given Jee main exam. Some of the preparation tips I am mentioning below which you can follow -

1. Know the syllabus very well.
2. Read standard books only as there are many books available in the market so it is advisable to use the books which make all your concepts clear and which are easy to understand.
3. Understand the weightage of topics properly.
4. Proper Revision plan should be followed.
5. Mock Tests and Practice Tests should be done as this will help you to learn time management skills and this will also make you familiar with the exam pattern.

Apart from this, you can check the complete Jee main eligibility criteria below as well -

Jee 2018 Eligibility

Hope this helps!!!