When replacing a head gasket, always mark and index all of the parts that are taken out of the vehicle. Also, check the service manual to see if it is better to remove each part separately or to remove parts as a unit.
Also, ensure the head and block are flat. A repair shop can fix cracks or adjust the flatness if needed.
Clean the threads, bolt holes and stud holes with an air compressor to make sure that the torque readings aren't thrown off by dirt or debris. Another tip is to make sure not to scratch the block when preparing and cleaning its surface to ensure that it seals properly.
When it's ready to install, pre-fit the head gasket, and only use sealant if the manufacturer requires it.
Before installing the bolts, coat them with engine oil. Also, use new bolts if necessary, and always ensure that the bolts have the proper torque.