How convert instances of a language efficiently into 3SAT instances?
The idea is to reduce an instance  $x$ to $\phi$ that uses only $O(T(n))$ symbols and clauses. $\log T(n)$ will be the length of binary representation of each symbol. This is the upper limit that you cannot cross if you want to solve the problem. So, you will have to optimize quite a bit. See the oblivious TM and state representation in Arora and Barak to get an idea.