Dried fruits are heavy and will sink if a cake mixture is too soft and wet. If the fruit has been washed, spread it out to dry well on a cloth before adding it to the cake mixture. Glace cherries are particularly heavy and covered in sticky syrup, so always wash, dry and quarter the cherries to make them lighter.
If you find the fruit still goes to the bottom of the tin, toss it first in a little flour or ground almonds. This technique should help to spread the fruit evenly throughout the cake.