If you are asked to give a referral to a candidate for a job, what are the things that u r gonna focus on his/her resume ?

Write what value the person brought to the company.
The strong character traits (hardworking, quick to catch up on technologies, no bullshit, natural leader) and you can also back it up with actual examples.

Or just copy/paste some other recommendation letter, I guess it works alright either way.

If you want to have the biggest impact, then focus on specific awards and achievements the candidate achieved rather than just saying words to the effect of "yeah they're really good".

Don't expect it to have a great impact though. Referrals are usually just a filtering mechanism - if they're crap or you can't get one, it's often game over, but you don't get any special advantage through having an "extra good" referral in most cases.