焼け石に水 It's like a mere drop in the bucket.

安物買いの銭失い　　　Penny wise and pound foolish.

柳の下にいつもどじょうはいない　　　A fox is not caught twice in the same snare.
(snare→「わな」の意）

藪をつついて蛇を出すな　　　Let sleeping dogs lie.
Wake not a sleeping lion.

病は気から　　　Care will kill a cat.

雄弁は銀、沈黙は金　　　Speech is silver, silence is golden.

油断大敵　　　Danger is next neighbor to security.

よく学びよく遊べ　　　All work and not play makes Jack a dull boy.

寄らば大樹の陰　　　Better be the tail of lions than the head of foxes.

弱り目にたたり目　　　Misfortunes never come singly.