Please let me know whether I should wait for jee mains or get admission in private colleges if I am confident to secure good in jee mains. But not sure to get IIT.

You have NITs, IIITs, GFTIs other than IITs. And you haven't mentioned your January score. But you can calculate your percentile using the formula 100-your percentile*869010/100 where in 869010 is the no.of Candidates who have appeared for January session. Now direct admission to Private Colleges should always be the last resort given the huge financial burden it might bring to the table. What we would suggest is wait for Sepetmeber session, see how you have fared and then take a call. If you can score 95 percentile and above, you will not need a Private College because then the opportunities would open up in good Colleges. And eitherways the Academic year has not started yet and so you have time to wait and take a call. If you are confident of scoring good in JEE Mains, you should take advantage of that;). May be this can help you in your preparation:

You need to know your syllabus and understand the exam pattern. Make a plan and stick to it. Make a note of the books to refer from and practise as many mock tests or sample papers as you can.

Divide the syllabus into Class 11 and Class 12 and the topics as "Need to Learn", "Weak" and "Strong". Now it is important to check the weightage of each topic. In Physics, Modern Physics take the top slot with 5 questions. Heat and Thermodynamics, Optics, Current Electricity, Elcetrostatics get 3 questions each. Magnetic has 2 questions and the rest get 1 question each. In Chemistry, Transition Elements and Coordination Chemistry, Periodic Table and Representative elements take 3 questions slot. Thermodynamics and Gaseous state, Atomic structure, Chemical Bonding, Chemical and Iconic Equilibrium, Solid State and Surface Chemistry and Nuclear Chemistry and Environment get 2 questions slot eacch and the remaining get 1 question each.In Mathematics, Co-ordinate Geometry gets 5 questions. Limits, Continuity and Differentiability, Integral Calculus get 3 questions slot each. The rest get 2 and 1 questions slot. For complete breakdown, please read our article: https://engineering.careers360.com/articles/jee-main-syllabus-weightage . Once you complete a topic, try to practise the concepts and write down the important points and paste them somewhere that you can see. Practise questions from that topic. Refer to books like:

Concepts of Physics by HC Verma

Fundamentals of Physics by Halliday, Resnick and Walker

Understanding Physics by DC Pandey

Problems in General Physics by I.E.Irodov

Understanding Physics by Freedman and Young

Problems and Solution of Physics by Shasti Bhushan Tiwari

Chemistry:

NCERT Books

Modern Approach to Chemical Calculations by R.C Mukherjee

Organic Chemistry by OP Tandon

Concept of Physical Chemistry by P Bahadur

Concise Inorganic Chemistry by J D Lee

Physical Chemistry by P.W Atkins

Organic Chemistry by Morrison and Boyd

Mathematics:

Objective Mathematics by RD Sharma

Plane Trigonometry by SL Loney

The Elements of Coordinate Geometry by SL Loney

Algebra by Dr. SK Goyal Arihant Publications

Play with Graphs by Amit M Agarwal

Differential Calculus by Amit M Agarwal

Integral Calculus by Amit M Agarwal

Integral Calculus by Amit M Agarwal

Complete Mathematics for JEE Main TMH

Important points:

You need to be physically fit to be prepared for what is ahead of you.

Keep telling yourself that you can. That is important

Make sure you improve on the speed in solving sample papers and quizzes

Take online mock tests

Focus on acuracy and speed as well

Improve your concepts and focus on weaker areas

Short breaks between change of subjects is really important

Do not overstress yourself

Avoid oversleeping during the day but get adequate sleep

Dont get nervous.