The dissipation factor of a capacitor is the power loss when AC is applied through the capacitor. This power is either absorbed by the dielectric material or internal/external resistance. Externally, the leads, pads, and solder all lead to an increase in resistance.
A high dissipation factor may lead to diminished life of the capacitor and cause deterioration of electrical properties of other components affected by the temperature increase. This temperature increase can be maintained with add on components such as fans and heat sinks but will add weight and cost.
The equation for the dissipation factor is the series resistance divided by the capacitive reactance or shown as DF = Rs/Xc.
Another term that you may see more is the Q factor or quality factor. The Q factor is the mathematical reciprocal of the dissipation factor; as DF decreases QF increases. Q factor can be found with capacitor reactance divided by ESR or Q = Xc/ESR.
To minimize the dissipation factor in your circuit you may need to choose a capacitor with a higher Q factor and reduce the resistance in the circuit. Some things you can do to reduce this resistance is increased quality of the pads and conductors. Clean solder joints will also help with the resistance. This would mean a change in the material, leading to higher costs but will produce better results.
Visit the capacitor section at Digikey.com to find the capacitor you need and find the information on the datasheets provided.