VISA is not a big problem, unlike the US VISA, only a few are refused VISA. The VISA form is available beforehand and you may fill it and take it with you. The officer mainly wants to confirm that you can fend for yourself in the months leading upto the examination and beyond before you get a job. They also would like to hear that you will return back to India when you are done with your training! You can show that you have reasons to return back (such a family house, a promise of a job etc)
A PLAB admit card is almost a must.. You dont need "no objection certificates" from anyone.
On some occassions the VISA officers have allegedly asked (unbecoming) questions, possibly due to a basic ignorance of the special VISA doctors have, to work in the UK. You should point out that doctors and dentists don’t need a "work permit", they can work on a "permit free training" type VISA.
On one occassion one of our boys was refused VISA as his English was not "upto the mark we expect of a doctor". On his behalf we explained that this doctor had passed his IELTS and that was proof enough of his skills in English, which the officer accepted and gave in.
At Heathrow, the VISA is but a formality, only those with forged documents are sent back.