Quarantine
When new succulent plants are aquired, it is a good idea to keep them separate from the rest of the collection for a few weeks so that obvious pests can be spotted. This allows time for eggs of pests to hatch and the progeny dealt with. A good way to do this is to maintain a "quarantine" window ledge separate from other plants. Many growers repot newly aquired plants into their favourite growing medium, and this is a good occasion to examine the general condition of the roots and check for pests such as root mealy bugs.
It may seem over-cautious, but many people like to treat their new plant with systemic insecticide while re-potting. This doubtless helps to avoid introduction of new pests into the collection. Repotting with "sterilised" compost which has been heated sufficiently to kill insects, larvae and eggs is a good idea.

Inspection
A regular check on the condition of your succulent plants, perhaps while you are watering them, will help you to spot the early signs of pests and diseases which are best treated early before serious damage is done to the plants, or before they can spread through the collection. However, never assume that just one plant in a collection is affected. Pests may well have spread to other specimens nearby, even if you can not see them. Ants "farm" mealy bugs for their honeydew secretions and may help to spread them through the collection.

Also watch how well individual plants are growing. Poor growth, a sudden change in condition or a limp plant which fails to take up water can be a warning sign of damaged roots caused by e.g. root mealy bugs, vine weevil, or roots rotting as a result of over-watering.
HygieneCleanliness in the greenhouse is an important measure in preventing outbreaks of pests and diseases. Always remove dead leaves and flowers as soon as possible. Some growers like to remove flower stalks of e.g. Adromischus before they flower and drip nectar on the plants, potentiating moulds. Leaf litter provides an ideal hiding place for pests. If wet by watering, dead plant material is a breeding ground for fungi and production of their spores. Tidy up debris in the green house left from re-potting and propagation. Treatment of the ground under the staging, walkways and areas of paving with a disinfectant solution e.g. Jeyes Fluid is a smelly but effective traditional way of discouraging pests and diseases.