Do you notice your toilet filling real slow after you flush it? The culprit is most likely the fill valve is worn or filled with sediment from the water.
The fill valve, is the tower inside the toilet tank where the water enters and has the float attached to it. It will sit off to one side of the tank. There are a number of different models that can be used, each with a little different configuration, that all attach in the same manner.
Replacing the fill valve is an easy project that requires a pair of water pump pliers and a sponge.
Check out this video and see how simple it is.