There are two types of microphone rustle. The first is noise from material touching and rubbing against the microphone directly, and the second is the sound of material making noise nearby and being picked up by the mic. To avoid the first problem it is best to attach a microphone to clothing rather than skin so the mic moves with the material rather than the material moving over the mic.
Sometimes, however, this can’t be avoided, such as when a character is wearing a thin t-shirt and the mic would be seen through the shirt. In this case, attempting to attach to the skin would be recommended. Alternatively, in this example, have your character wear an undershirt and mount to that). It may be possible to attach the microphone to a thin shirt by hiding the mic behind a pocket in a pocketed t-shirt or camouflaged by a screen printed logo or design.
Other common issues mounting lavalier mics include men with hairy chests and women with low cut tops. Chest hair can cause a rubbing noise that mics can pick up. If this is a problem try to have the talent wear an undershirt to act as a barrier to the hair. For women with low-cut tops, if they are wearing a bra, try hiding the mic in the middle with it peeking out of the top. Make sure the mic isn’t completely covered. It may be possible to tape the mic to the bra.
Wherever possible the sound mixer should be monitored for these problems during shooting, as clothes can shift.