Multicellular organisms, which were probably doing meiosis, would have had a greater genetic diversity (meiosis) and more capabilities to exploit new habitats (size, morphological diversity), this multicellularity having arise just before the Cambrian explosion. Further, the climate during the Cambrian was mild and favorable to range of life forms, compared to the climate immediately before.
Work Step by Step
First think about what happened just before the Cambrian which could have been fuel for the evolutionary fire during that time. The consider any features of that time which were generally favorable to life overall.