The best practice here is to pay for what value you consider the employee will be able to add next year. Some factors to consider are:
1. What do salary increase surveys from analysts say?
2. How has company performance been and what does the forecast look like? Obviously, if you expect to grow at say 20% but you're offering your top performers 4-5%, that's going to be unfair.
3. Build in differentiation. Is there sufficient difference in the hikes provided to people you consider are going to be top performers and the rest?
4. Like @Wristy said, you'd want to factor in internal equity too.
I'm not a huge fan of building inflation adjustments into pay increases, but that depends on individual company strategy.