How to prepare costing??

Same here.

I think you need more practise. The value of answers have reduced recently and thus we have to know the answer as soon as we see the question. So you are supposed to solve every Question at least 5 times (i.e.PM+RTP+Any other class notes you have)

There will be overlapping and that will make task somewhat easier.

Concentrate on answering first than form.

Also this time theory might come and it surely requires less time so do that too.

I am going to do above mentioned things and you try to do it too, see if it helps.

If you can join a CA whatsapp group it would be great and then we can both share our progress.

Otherwise see if you can go to a library and study with other people, it surely helps when 2 or more people do costing together.