The first thing we need is trust and for that we need an unhindered engagement in talks. Unless, the governments on both sides show that they are committed to resolving the issues plaguing our relation regardless of what happens, it will be impossible to move on as we have been observign for so many years.
I think India can start-off by saying that peace talks will be impervious to terror. I am not saying that terror as an issue should be off the table. But doing so would deter the anti-India elements in Pakistan on the one hand and give enough ground to the government to take action. What has so far happened is the exact opposite and that enables these elements to get the upper hand as if they dictate the terms on how Indo-Pak relations should move. Also, include Kashmir as core issue. This will help even more than the first.
Pakistan, on the other hand, can start-off by giving a guarantee that no terror from it's soil will be directed towards India. Not just the rhetoric that we won't allow our soil to be used by terrorists.
Both can find several common grounds of interets. Economy, culture, sports etc. Let's move on them while we sort out the bigger issues. This will set the pace.
I don't think there is or should be any room for outside interference. The only party to this dispute is China and i don't think India will be happy to see it meddle. And it has often said that it wants the dispute to be settled between the two countries.