常见的idioms有:

1)act like a pro: 做事很内行

He's only a high school student but on the baseball diamond(棒球场)
acts like a pro; today he threwa no-hitter.(投了一个无法击中的球)

2)bite off more than one can chew:
字面的意思是"咬下比所能嚼碎的更多的东西". 引申为"力不胜任".

I advice you not to try to work at a full-time job and go to school at the same time. You'll
be biting off more than you can chew.

3)hold one's own  坚持到底, 寸步不让own的意思是that which belongs to oneself.亦即自己的position( 立场）,condition(条件)等.
本习语使用最多的场合是:
       "尽管对手强","尽管情况不利"或者"尽管自己处于劣势",而要hold one's own(坚持到底,寸步不让).有时,表示"虽则痛苦,但能坚持".

Though our team lost in the end, it succeeded in holding its own against a much stronger opponent for most of the game.

4)land on one's feet  安全摆脱困境原意是"象猫一样,掉在地上也会脚先着地".现转用于表示"虽然陷入困境,但是顺利脱险'的意味,使用范围极广.

We were very lucky. A wonderful new job offer right after my husband's company went bankrupt allowed us to land on our feet.

5)on the ball  能胜任从be on the ball演化而来.be on the ball是指"站在球上",所以要时刻当心不要掉下来. 所以, 它的意思是"全神贯注".一个人, 一旦能全神贯注地投入,他一定能胜任某一项工作, 所以有了on the ball的这个意思.

I think you should hire him; he's got a lot on the ball.

6)out of one's depth 力所不及one's depth 是"有自己身高那么深的地方", 所以本条的原意是"处于身体站不住的地方".

I never should have tried to enter that college. The moment I saw the entrance exam I knew I was out of my depth When our literature professor digresses on astronomy, he's out of his depth.

7)be right up one's alley  (正是某人的)特?alley是"小巷"的意思.原意是"正在顺着(某某
居住的)胡同走上去"从"自己熟悉而且关心的地方"这一想法出发,便演绎为"正是自己所能并关心的东西","拿手好戏".也可以说"be right down one's alley".

If it's a book on mushrooms, why not get Mr. Whitestone to write it? That'd be right up his alley.