I learned this tip from another agency and it has been very useful:
During a vehicle search, if you find something that will result in an arrest--like drugs, weapons, etc.--pass by it. Shortly after, start walking back towards your cover officer and while walking, scratch your badge.
Why your badge? Because it doesn’t itch. This will give the cover officer the tactical advantage of knowing that the subject he is watching is about to be placed in custody.
Discuss this tactic with officers at your agency. Most of the time your cover officer is the only one who doesn’t know what has been found in the car, putting him at a serious tactical disadvantage.
Also, instruct your cover officer to continously talk to the subject he is watching, regardless of the topic, and while doing so, to watch for any movements or indicators showing the subject’s interest in a particular area of the vehicle. If nothing is found, allow the cover officer to search the areas the subject showed interest in while transitioning the initial search officer into the cover officer.