Axelrod's properties of a successful strategy (like TFT):
nice — it is never the first to defect
retaliatory — cannot be exploited by non-nice strategies
forgiving — willing to cooperate even with those who have defected against it (provided the defection was not in the previous round; TFT would defect in this case)
clear — easier for other strategies to predict its behavior to foster mutually beneficial interaction
Wikipedia says this about how to find an optimal strategy for IPD:
Bayesian Nash Equilibrium: If the statistical distribution of opposing strategies can be determined (e.g. 50% tit for tat, 50% always cooperate) an optimal counter-strategy can be derived analytically.
Monte Carlo simulations of populations have been made, where individuals with low scores die off, and those with high scores reproduce (a genetic algorithm for finding an optimal strategy). The mix of algorithms in the final population generally depends on the mix in the initial population. The introduction of mutation (random variation during reproduction) lessens the dependency on the initial population; empirical experiments with such systems tend to produce tit for tat players, but there is no analytic proof that this will always occur.