First of all it is great opportunity for one who wanted to make career in ISRO where dedicated research n technology advancement results fruitful career.

Well,I have been through many previous year question paper and pointed out some points which I would like to mention:

1. You must have basic knowledge of your domain eg. I do remember like once they have asked question like,~ If you remain open the door of refrigerator then what the condition of room would be?.So must have to deal with the application of what you study.
2. Question that they are generally 15–25% are theoretical,which includes some formula based n some application based.
3. Around,60–80% question includes numerical part. One can score good in this.They generally ask moderate n easy question, generally answer comes in 2–3 steps.
4. In addition they do use direct Gate previous year questions.

Now how to attempt question paper:-

1.In 90 min u just consider 80 min,as 10 will take u to fill the OMR

2.Here,accuracy plays a vital role than speed.You may get some tricky n lengthy question,but u should go first with the 1 st point question that I have mentioned above.

3.Next,you start medium n 2–3 steps question which is majority. Eg. a mechanical guy can skip SFD,Deflection etc. if they asked numerical.

4.Here,try to approximate your calculation, as some questions involves lengthy calculation.

5.If you attempt 70% questions with 85–90% accuracy then you are surely get in.

For mechanical earlier cut-off was:

2017: 119/234

2015:133/234.

So you need 55–60% marks.

Do previous year GATE,ESE- Prelim question papers.

Apart from that, I have also started daily MCQs course on different topics.