Few of the common mistakes people do while home composting are:
Moisture content is not maintained
Brown waste (dried leaves / grass etc.) is not added enough
Not adding enough compost maker.
Addition of animal and fish bones to the bin
Opening the cover of the bin too often, for addition of even small waste.
Addition of foul smelling rotten leftovers to the bin
Not giving enough for the process of making compost to naturally complete.