Consistency is the key.
Wanyama's first touch was poor, the ball was taken from him, he dived in two footed from behind and didn't get the ball, arguable a yellow but he gave Clattenburg a decision to make. It was stupid. However, Valencia's challenge was just as bad in the grand scheme of things.
Clattenburg loves the attention and getting his face on tv. Another ref and a 3pm kick off and he might have got away with a yellow, but the point still stands, don't give the ref the opportunity to send you off!