I am in class 12 .How can i manage both state board public exam and neet exam preparation simultaneously?

The basic concepts present in college and NEET syllabi are slightly different with NEET having NCERT concepts. Ensure that you're thorough with college syllabus, this will strengthen your foundation for NEET. Talk to your guidance counsellors or trusted education consultants if you think you need help.
Preparation for NEET involves a lot of aspects:
- BOOKS: Please follow the link https://www.careers360.com/question-to-score-top-ranks-in-neet-which-book-should-be-preffered?icn=question-title-details&ici=topic-detail-page - PAPERS: When you practice these papers, solve them in a mock exam format and analyse your papers after that, outlining strengths and weaknesses. These questions are seldom repeated, their main purpose is to develop time management skills. Here are some links: https://www.entrancecorner.com/medical/articles/neet-2018-sample-papers/ http://www.careerpoint.ac.in/free-sample-paper/neet-sample-papers-download.aspx https://medicine.careers360.com/articles/neet-sample-paper
- STUDY MANAGEMENT:
1) Skills: Everybody shows a diversity of study skills and tactics. To know how you learn best, check out this site, http://vark-learn.com/ It contains a questionnaire that will tell you your learning preference and various strategies to strengthen it further.
2) Habits: You need to figure out which duration of the day you attain your peak concentration levels and do the most difficult topics during that time. Study the other topics during other timings. Also, figure out which place is most ideal for you, clear of things you find distracting. 3) Planning: The old saying, "If you are failing to plan, then you're planning to fail" applies here as well. It saves a lot of time as you have an agenda of what you want to accomplish. Don't be disheartened if you are not able to complete one of the goals, no plan can be 100% perfect. I recommend, not to make rigid plans, keep it flexible
- MANAGING YOURSELF: Preparing for this exam is not an easy feat but it is a learning experience. You should also enjoy and keep yourself happy, otherwise a bitter attitude will take a toll on you later

I would suggest you to go through the below tips  - Know the syllabus as most of the syllabus of Boards and NEET would be the same except few topics - The first thing which you need to know is the complete syllabus and accordingly prepare. Important topics- Physics – Optics, Mechanics, Nuclear Physics, Thermodynamics, Chemistry – General Organic Chemistry, Mole Concept, Periodic Table, Coordination Chemistry, Chemical Bonding. Biology – Genetics, Ecology & Environment, Cell Biology, Morphology, Basics of Biotechnology, Reproduction, Physiology of Animals & Plants. Good Study Material - The most important element to prepare for any exam is good study materials as better to choose the standard preparation material.
Create a time table as per your schedule - Get a calendar and a diary, set your priorities, set out long study hours. Take care of your health. Don’t sleep during study time.
Practice NEET sample papers and previous year’s question paper - All NEET aspirants should do practice on sample and previous years papers as these would be helping them to know the important questions. Prepare notes - The best way to improve memory skills is to prepare notes while studying. Candidates should write down all the important notes in a copy or diary which can be useful for revision before the examination and save a lot of time for them. Online mocks - It would be better if you complete your syllabus till December and keep Jan-Feb for your sample papers and previous year papers and once you are done with these, start doing online mocks because these will be showing you all your weak areas along with actual paper pattern and accordingly you can practice again and this will also teach you time management skill during exam. Apart from all these, better to be confident and do not cram. Books which you can refer - Biology: NCERT Biology of Class XI and XII, Trueman's Biology Vol 1 and 2,Objective Biology by Dinesh, Pradeep Publication's Biology, GRB Bathla's Publication's for Biology. Physics: Concepts of Physics by H. C. Verma NCERT- Physics Part 1 and Part 2 D C Pandey Objective Physics Fundamentals of Physics by Halliday, Resnick and Walker Problems in General Physics by I. E. Irodov. Chemistry: NCERT Chemistry Physical Chemistry by O.P. Tandon Organic Chemistry by Morrison and Boyd for Organic Chemistry Modern’s ABC of Chemistry for class 11th and 12th Concise Inorganic Chemistry by J. D. Lee for Inorganic Chemistry Dinesh Chemistry.
Hope this helps!!!!

You have to study18 hours a day.work hard only then you can manage both.