If you don't have any ready-ground spices to hand, place them whole into a spice grinder and grind them into a powder - or alternatively use a pestle and mortar.
Super simple: Mix the spices together in a small bowl. Store the mixture in a closed jar or spice container.
Notes
If you don't have any ground allspice or cloves to hand, then add some regular dried cloves or allspice to a spice grinder to grind them into a powder. Best put the powder through a strainer to filter out any larger bits before blending your spice mix.