Vegas is a city that runs on tips. It's no different checking into your hotel, where a discreetly placed $20 bill - sandwich it between your photo ID and your credit card- will often earn you an upgrade.
FrontDeskTip.com ranks major Vegas hotels by how likely tipping the check-in clerk is to get you an upgrade, based on users' field reports.
You have to tip frequently in Delhi but only small amounts like 20 or 10 rupees. But these bills seem to be hard to find, so whenever you get a chance, get hold of these bills because you will need them.
There's an excellent video which talks about a few other travel tips in Delhi: www.geobeats.com/videoclips/india/new-delhi/traveling-tips
When visiting a city like Delhi, I found travel preparation even more important than usual.
All around Delhi
Remember that most Thais earn very little; they are getting by on 100 Baht a day - about £1.20. I never tip less than this. It is little enough to us, but a day's wage to a Thai. Go on, just do it!