JEE Main

Well you are scoring 139 marks, it means according to last year's statistics your AIR will be around 33k. With this rank forget about any good in top NITs but you can get low-level NITs such as NIT Srinagar, NIT Uttrakhand, lower branches in NIT Hamirpur, NIT Jalandhar.
If you are CSE or ECE aspirant then you can try in new IITs which are running under NITs such as IIIT Una, IIIT Ranchi, IIIT Naya Raipur, IIIT Surat, IIIT Bhopal in these colleges you will get these branches but don't lose hope till last round.
You can try for civil engineering in PEC.
All the best

Hi Mahipal,
You can use the JEE Mains 2018 college Predictor option available on Shiksha. Com. College Predictor helps students to get an idea about the chances of admission in the college of their choice based on JEE Mains 2018 result. Please refer the link below for your reference:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor.

Hi Rama,
You can use the JEE-MAINS 2018 College Predictor option available on shiksha.com. College Predictor helps students to get an idea about the chances of admission in the college of their choice based on JEE-MAINS 2018 result.
Please refer the link below for your reference:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor

If PCM score is 50%, then you can get admission in ICEM. Your JEE score is less, so you can apply for the direct admission process.

You have to score at least 75% in class 12th to get a seat in IITs and NITs. You have to give re-exam to get a seat.

Yes, it is compulsory to clear cutoff of every subject to clear JEE advance. You cannot qualify JEE advance with the help of one or two subjects. The cutoff of every subject is class 12-14 marks per subject, which can vary depending on the cutoff.

First, you should try to get college in the counselling, and also not only of JOSAA, but also of your state level counselling, which is conducted by department of technical education of your state to get any good government colleges of your state. If you won't get any good college, then you can take a drop.

Your rank is too low to get NIT. You have to satisfy with any government college or private college in your state. Try to get government colleges for this you can wait for 2nd round of counselling, if you won't get in first round.

For JEE Mains, it is enough to solve NCERT, MTG Maths and practice previous year papers. You can also practice from SL Loney (for trigonometry). For JEE Advanced more practice is required from slandered books.

It is very tough to say, unless you have some category, but still category won't ensure you a seat. The best thing to do, is to check Shiksha college predictor.