Former India opener Aakash Chopra is the author of three books, the latest of which is The Insider: Decoding the craft of cricket. @cricketaakash
Judging the length the moment the ball leaves the bowler's hand and trusting in your own defensive game are keys to starting a new innings on Indian pitches. At least in the first innings of a Test match. Perhaps you could also go on the offensive from the start and build an innings but that option is more risky.
Even the most aggressive batsmen against spin need a tight defence to survive against it in India. Even if you were to score a run-a-ball century in a Test, you won't play more than about 30 scoring shots on average. The remaining 70-odd balls are to be played with caution.
Back to Root and how he started: for that was as critical as the wide range of strokes he displayed in his double-century (and his 32-ball 40 in the second innings). The ball hadn't started turning viciously by then and the bounce wasn't alarming either. A couple of times he played Ashwin's deliveries for turn but found the leading edge, which took it towards covers. He also went back to a couple of deliveries that were fairly full but eventually, and wisely, played them defensively. Coaches advise that a batsman must never commit two mistakes on the same ball: if you have misread the length, don't follow it up with an attacking shot. Playing it defensively is your best response after committing the first error. Root did just that.
The other thing Root did was, he didn't go on from where he'd left off in Sri Lanka. He had swept his way to back-to-back hundreds (including a double) there only a couple of weeks before. For a batsman to have scored the number of runs he did in that series, one might have been lulled into believing the new innings didn't require the same process and hard work.
The most striking feature of the first 30 or 40 balls Root played in Chennai was how he stopped himself from using the sweep. It was important to understand the pace and bounce of the surface, for only then would he know if the sweep was the only scoring option. Of course, the stroke wasn't necessary in the first innings but it was critical for success in the second. Root bided his time in the first innings and imposed himself only on the inexperienced duo of Shahbaz Nadeem and Washington Sundar, but in the second innings, he went after Ashwin straightaway. The knowledge of when, how and against whom to score was the heartbeat of Root's batting in the Test.
After the cautious start in the first innings, he showed how robust his game plan was against both spin and pace, and that he was totally committed to it. In his knock of 218 runs, he hit only three boundaries against the fast bowlers. He understood that most deliveries would end within the stumps, and so he ensured his head never went too far outside off when playing his strokes. His front-foot stride was negligible but very straight, with the toe pointing down the pitch, allowing the bat a free path to meet incoming deliveries. While a long forward stride is advisable to negotiate conventional swing, it's counterproductive when you're tackling high-quality reverse swing; Ajinkya Rahane's dismissal in the second innings is a fine example of this. Sometimes less is more.
Barring the first half hour, Root hardly ever misjudged the length. He went forward to everything that was fuller but was quick to use the depth of the crease to create scoring opportunities off the back foot. He did that a lot against Nadeem and Sundar, sweeping frequently. He did acknowledge the Ashwin threat and treated him with due respect (though not too much) but he didn't miss out on a scoring opportunity against him either.
A lot of overseas batsmen are guilty of playing with hard hands and going too low, or both, in India, but Root has been exceptional on those counts, playing with soft hands while defending and never going too low - for that leads to the ball potentially hitting the splice of the bat or the gloves).
His wide range of sweeps are a result of him picking the right length quickly, for sweeping is all about first choosing the right length and then bringing the bat down on top of the bounce to keep the ball along the ground. Root rarely found himself too close to or too far from the ball while going down to sweep. And he didn't hesitate to play the reverse sweep too, when he grew in confidence.
India need to look for weaknesses in his armour, if any. For starters, I feel that they will prepare a pitch that is spin-ready from day one for the upcoming Test, for that will pretty much nullify the advantage of winning the toss. Secondly, the Indian fast bowlers must bowl the fourth- and fifth-stump line more often, for someone who is prepared to play inside the line all the time is a little vulnerable against deliveries outside off. That plan might also drag him towards the off stump, and that in turn might open up the chances of an lbw a little more. As for spin, he seems to have a good measure of the conditions and all the Indian spinners already, so it would seem to call for just sticking to the basics for as long as possible. If you can't prise out a batsman tactically, you must tire him out with control and discipline.