That's a very big question that relies a lot on how he actually came to power. Because trotsky spent his career scorning the middle strata of the beauracracy that put Stalin in power. How does he beat them?
The question though of "what does he do if he comes to power" though can probably be answered pretty easily because he answered it himself in The Revolution Betrayed. And generally summing that up Trotsky's policy would be very different in key aspects, first and foremost being that he was against the power of the bureaucracy and will almost certainly try to destroy their political influence and power. His international policy is up for grabs really depending what you think of Permanent Revolution, I'd say the likeliest reality is that he'd be the head of what would remain a pariah state outside of communist led governments, but his leadership of he Commintern might mean there's actually another communist revolution in Europe (in which case all bets are off because then Soviet Policy shifts from being leader of the revolutionary cause to being an ally of a more advanced revolutionary nation, which will also likely totally shift the balance of power across the Soviet Union because it means that things are immensely easier for them on every economic front).
Assuming that doesn't happen though, he was in favor of gradual collectivization primarily of large estates rather than hard and brutal total collectivization (which he considered to be a reckless policy that served to bring back the conditions of the civil war for little gain). He was culturally libertine and in favor of modernistic ideas about science, sex, and culture. So the Soviet Union is unlikely to re-illegalize homosexuality and "conservative" art like ballet, realist painting, and classical music are unlikely to receive nearly as much state sponsorship. I half expect some kind of compromise on the NEP which kills the NEP Men but retains semi-market relations (probably with some kind of state managed distribution corporation replacing them). The Army will face a major restructuring.
With the pressure off of civil war Trotsky fully intended to restructure the military along more socialist lines. Stuff like officers being elected for training over a proper professional officer corps, the abolition of Officer privileges, the use of skilled Soviet officers from the civil war training a new officer corps, and the adoption of something similar to Revolutionary War Doctrine from Reds as the official war policy.
In my opinion all of this is better policy than what Stalin ended up putting in place. But I'm a Trotskyist so that's kind of obvious that I'd have this position.