策略 is a broader term for strategy or scheme, not necessarily deceptive; 瞞着手段 specifically emphasizes trickery and deception.
ごまかし is a more casual, everyday word for deception or covering up; 瞞着手段 is more formal and implies a planned method.
Compound of 瞞着 (manchaku, 'deception') and 手段 (shudan, 'means, method'). 瞞着 itself is a Sino-Japanese word combining 瞞 (man, 'deceive') and 着 (chaku, 'arrive, wear'), though the exact historical derivation is uncertain.