I'd first check to see if the domain is listed for sale on Sedo or Afternic. If so, put in an offer that way.
Otherwise, you will need to email the domain owner. I'd recommend including an offer, as a lot of people simply ignore emails that don't include a firm offer. You probably want to research the owner on Google - it might help you craft a better email.
I wouldn't add in anything about the purpose or transfer details, etc.
Well if you can't get LLL.in - since everyone would expect to make a good $xxxx on their investment, i would suggest to opt for other variations with .co.in / .firm.in or .org.in etc 3rd level extensions.
Brands need to be created, just by LLL.in wouldn't guarantee hits to the site, so you might as well build brand for your .co.in or others. Utilize the money saved - by investing in brand building.
This is decent advise, but its shortsighted. What will this end user do after he has bought that mediocre .firm.in, or even .co.in,developed it and it starts getting "hits" and realizes that the .in is still not owned by him? This is where the end user has little leverage and will get at least partly mauled financially when trying to acquire that .in name.
My point is- If you as a domainer wants to buy an lll.in from another person, follow what Jeff said- make an offer in your email. ALso, make your honest, best offer, because whether the offer is accepted or not,thats the best you can do!