What two environmental conditions would preserve soft body parts?
For preservation of soft body parts as fossils in rock, burial, and an anoxic (lacking Oxygen) Environment are necessary.
Burial provides a medium in which to preserve the body parts.
A lack of oxygen (anoxia) will prevent all biologic activity, such as decay or predation, allowing the buried body part to survive long enough for mineralization (gradual replacement of original biological matter with minerals such as quartz) to occur.
Anoxic conditions are relatively rare on a geologically significant scale; they exist usually in stagnant water, where biologic activity has depleted the oxygen supply, and no fresh water flows exist to clear out and replace the anoxic water.
If your question is about peserving actual soft body parts, not as fossils, the answer is that dry and cool conditions, or freezing conditions, will retard decay, and thus will preserve organic material such as soft body parts for a time.