Exposition can be lowered by performing your actions at night, or by simply not doing anything during the day.
Exposition will increase if you perform illicit actions in daytime : drug deliveries, money runs, sample giveaways or getting caught by police.
DEA Risk and Raids
Once your exposition level has reached Terrorist, you begin to run the risk of attracting the attention of the Drug Enforcement Agency (DEA). Attract too much attention and you may become the target of a DEA raid. DEA raids do not come entirely unannounced, however, as a black van will be parked on the street nearest to one of your hideouts, signaling that, upon entry to your hideout, a DEA Raid will begin.
See Also: DEA