While making vegetarian mincemeat I found myself short of some mixed spice, so set about making some more from spices I had in stock. 

According to wikipedia the following spices are commonly used in mixed spice:

Cinnamon
Nutmeg
Allspice
Mace
Cloves
Ginger
Coriander
Caraway
Cayenne Pepper

Depending on the desired taste any of the ingredients can be used in varying quantities, although its best to always include some of the first three.

The quantities I used were as follows:

1 tbsp cinnamon
1 tsp grated nutmeg
1/4 tsp allspice 1/4 tsp cloves
1/2 tsp ground ginger
1 tsp coriander seeds

I grated the nutmeg with my extremely efficient microplane nutmeg grater, and ground the other ingredients together using a nice solid morter and pestle.

The resulting spice should be sealed in an airtight jar and used up within a few months  if possible.