Hello,

There are books that are recommended as better ones for mechanical engineering for gate which I am going to mention below. But I would suggest you to follow the hand written notes (which can be downloaded online) from various coaching institutes. Because, the text books have all the matter included and if it is from the coaching institute then they will guide you properly  on which of the chapters, you have to put more stress and also the problems materials, they provide is quite helpful and they aree like the model ones like in the gate. Here are some link and books, that will help you

Coaching Institutes:

ACE:

https://www.gatexplore.com/ace-academy-class-notes-mechanical/amp/

MADE EASY:

https://www.gatexplore.com/made-easy-class-notes-mechanical/amp/

S. K. MONDAL:

https://www.gatexplore.com/download-s-k-mondal-mechanical-engineering-notes/amp/

General books:

Design of Machine Elements-

• Machine design - V.B. Bhandari

Engineering Mechanics-

• Engineering Mechanics by Bhavikatti
• Engineering Mechanics by Beer and Johnston,
• Engineering Mechanics by R K Rajput

Fluid Mechanics-

• Fluid Mechanics by R K Bansal
• Fluid & Hydraulics- Modi and seth

Heat Transfer-

• Heat and Mass Transfer by J P Hollman and R C Sachdeva
• Heat Transfer by Cengel and Holman

Industrial Engineering-

• Industrial Engineering by O P Khanna, Buffa and Sarin

Manufacturing Engineering-

• Production Technology: Manufacturing Processes, Technology and Automation by R.K. Jain

Strength of Materials

• Strength of Materials by Gere and Timoshenko, B C Unamia, Sadhu Singh, Ramamrutham

Thermal Science

• Engineering Thermodynamics by P.K. Nag

Thermo Dynamics

• Engineering Thermodynamics by P K Nag and Rajput
• Thermodynamics by Cengel.

Theory of Machines

• Theory of machines by Ratan

Vibrations

• Mechanical Vibration by Grover

To know more about the topics that are to stressed and preparation strategy  please go through the following link 

https://engineering.careers360.com/articles/what-are-best-books-for-gate-me

Hope this helps....