A Board of Appeals consisting of five members and three associate members shall be appointed as provided in MGL c. 40A, § 12, as amended, which shall act on all matters within its jurisdiction under this bylaw in the manner prescribed in said section and subject always to the rule that it shall give due consideration to promoting the public health, safety, convenience and welfare, encouraging the most appropriate use of land, and conserving property values, that it shall permit no building or use injurious, noxious, offensive or detrimental to a neighborhood, and that it shall prescribe appropriate conditions and safeguards in each case.