My name is Rahul Singh Sir I got 85 % in icse 10 and 83% in cbse 12 how can I prepare for jee main and upsee so that I can get a top government engineering college of btech please give some tips.

You haven't mentioned in which year you're going to appear for Jee Main whether 2020 or 2021. If you are going to appear for Jee Main 2020, the now only a month is left for Jee Main and now focus more on important chapters that means which carry more weightage. Instead of choosing a random topic from the syllabus, you must break your preparation into sections. Sub-topics from each section should be selected and then strategy on clearing concepts must be made. You can make short notes on the topics that you have find difficult to understand.
Never leave any concepts doubtful or unsolved. Once done with the syllabus and concept clarity, you should move towards solving previous years papers. Give mock tests as much as possible. Time management is one more important thing you should look upon. Remember that practise will increase your efficiency.
Give at least two mock tests every week. Then analyze your weak parts and work on them. If you find it difficult to prepare from books like HC Verma, DC Pandey, then only go for NCERTs. From wherever you study, you must complete NCERT Textbooks as many questions are directly asked from NCERTs.
Some important chapters you must focus on- For Physics, Rotational Motion, Thermodynamics, SHM, Electrostatics, Magnetism, Optics, Modern Physics. In Mathematics, Complex Number, Conic Section, Circle, Calculus, Vector & 3 D, Probability, Trigonometric Equation, Properties of Triangles, Quadratic Equation, Sequence and Series, Permutations and combination. In Chemistry, you can more focus on these chapters for last month preparation- Chemical bonding, Electrochemistry, Coordination compound, Salt analysis, Ionic equilibrium, Thermodynamics & thermochemistry, Aldehydes and ketones, Aromatic hydrocarbons, GOC isomerism, Liquid solutions, Alkyl halides and aryl halides. Beside this, give mock tests regularly.
But if you are going to appear for Jee Main, Next year, then you should wait for the syllabus to know. CBSE has reduced the syllabus from Class 9 to 12 by 30% and NTA has not yet announced any such notification to reduce the syllabus of Jee Main also. But it seems the syllabus of Jee Main and Neet will also be reduced keeping the core concepts unchanged. The topics which carry less weightage may be eliminated from the syllabus of 2020-21 session. The chances are quite high. But until NTA releases any notice, it can't be said properly. Please to hear this from the authority. For now you can prepare from NCERT textbooks.