Pitches in the subcontinent are believed to be tailor-made for spinners, which is why it's natural for overseas spinners to get excited whenever they travel to this part of the world to play. It presents them a rare opportunity to play the lead role in their bowling attack - as against mostly being defensive or restrictive while playing at home.
While this observation might broadly be correct, it rarely plays out so well for overseas spinners while playing India in India. Given the spin-friendly pitches (read, very little assistance for the faster bowlers in terms of bounce and lateral movement off the surface) the workload of visiting spinners increases manifold, but most, including some of the more competent ones, realise that their hard work isn't always rewarded as much as they might expect. Indian pitches encourage spinners to try and bowl magic wicket-taking balls every time they roll their arm over but most spinners end up being either too expensive or ineffective.
The key reasons for this are how slow the surfaces are, and how well Indian batsmen are able to counter spin. The lack of pace off the surface allows the batsmen to play the length, and since the typical Indian batsman grows up on a healthy diet of spin, they are able to strike the right balance between attack and defence.
So how should Dom Bess and Jack Leach bowl against the Indians? In my opinion, that's where the series will be decided - how the English spinners bowl to the Indian batsmen. If they complement their fast-bowling attack, England will compete, but if they fall apart, like many other spinners in the past, India will bulldoze their way to another Test series victory at home.
While Bess and Leach found success in the recently concluded series in Sri Lanka, it's probably safe to say they will be countering a more organised and competent attack from the Indian batsmen.
Let's start with Bess, a right-arm offspinner who bowls a little flat in the air and prefers to bowl the line outside off. His game plan is to go roundarm every now and then to bowl the arm ball that slides, instead of turning, after pitching. Inducing the outside edge is his key wicket-taking tactic and that seems to work fine in England, where the pitches aren't spin-friendly, by and large. The fact that he rarely bows long spells, and that batsmen tend to go on the offensive the moment they see a spinner in those conditions, make the away-going delivery potent there.
But that's not a tactic that works as well in India because of the slow pitches. The arm ball doesn't skid as much after pitching, and Indian batsmen typically use those deliveries to open up the off-side field for scoring. The one thing that you simply must not do as a spinner in India is allow the batsman to score on both sides of the pitch. When that starts to happen, it's almost impossible to seize control back, which in turn will mean Joe Root will need to ask the fast bowlers to bowl a lot more than they should in these conditions.
The pace at which Bess bowls is ideal for Indian surfaces, but he doesn't have the kind of control that, say, Graeme Swann used to have, and that's why it might be better for him to be more pragmatic about the role he is likely to play and reconsider his line of attack. It wouldn't be a bad idea for him to bowl everything within the stumps and have an in-out field throughout. Going by how he bowled in Sri Lanka, there will be a few loose balls on offer, and if all those deliveries are dispatched for boundaries, the Indian batsmen will run away with the game quickly.
On the other hand, Leach's stock ball pitches and finishes within the stumps. He tends to go to the edge of the crease often to create the angle that makes batsmen play against the spin, but trust the Indian batsmen to not be fooled by that tactic too much. The key to his effectiveness will be consistency of length, for anything too full or marginally short will be taken for runs. Indian batsmen are quick to convert a slightly short-of-length delivery into a ball that can be cut or pulled - that will be Leach's biggest challenge to counter.
While the Indian batsmen will be quick to use their feet to come down the track and also to go deep in the crease, most, barring the likes of Rohit Sharma, are unlikely to sweep a left-arm spinner. So that's the length Leach must bowl steadily for long durations to stay in the contest. And it wouldn't be a bad idea for him to bowl over the stumps and into the rough with a packed leg-side field later in the games.
The English spinners have their job cut out, for it's not easy to make changes to basic skill sets and tactics for an extended period, especially when you don't see tangible returns in the form of wickets - and it's more or less certain that Indian wickets aren't going to fall in heaps to the spin of Bess and Leach.