A No-Brainer

Example 1:

Bill: Do you have plans for vacation, Mike?
Mike: Nope. I can't decide what I want to do. My roommates want to go to Las Vegas, but my parents want to take me on a cruise through Mexico.
Bill: Mike! That's a no-brainer! You can go to Vegas anytime! The cruise to Mexico is something you shouldn't pass up.

Example 2: 

Seth: Have you heard back from the company you interviewed with last week? I know you've been looking for work for a few months.
Ruth: Yes, actually. They called me the other day to offer me a position.
Seth: Wow! That's great! You're going to take the job, right?
Ruth: Of course! It's a no-brainer!

Explanation:
A no -brainer is an extremely easy question or decision to make.
In Example 1, Mike has to decide between a trip to Las Vegas with his friends or a cruise to Mexico with his parents. While both trips sound fun, Bill thinks the choice is obvious and easy to decide- of course he should go to Mexico! Living in southern California, Mike has plenty of opportunities to travel to Las Vegas, but it's unlikely his parents will take this same cruise again.
In Example 2, Ruth says she will take the job. To her, there is no other option. It is the obvious choice.
You can think of something as a no-brainer if someone who has no-brain can still make the decision easily.

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To Take Something With a Pinch/Grain Of Salt (used as a verb)

First Example:

Lucy: Did you go to that political rally last night?
Jason: Yeah, and it was amazing! She had such great ideas, and her campaign promises are really inspiring.
Lucy: Maybe, but make sure you take anything she says with a pinch of salt.
Jason: What do you mean?
Lucy: Well, she's a politician. They're known for promising things they can't actually deliver just to get more people to vote for them.
Jason: I know, but I think she's for real.

Meaning: 

To "take (something someone says) with a pinch of salt " is a phrase that means you should be critical of what a person says. This idiom is often used when the person who says it doesn't trust something another person said, or thinks they have an ulterior motive.  In the example, Jason is excited by a political candidate, but Lucy says he should take what she says with a pinch of salt, suggesting that the candidate may be promising things she doesn't intend to deliver on.  
In addition, the word "grain" is sometimes used instead of "pinch." The idiom means the same thing with either "pinch" or "grain."

Here is another example:  
            
Bill: Want to try that restaurant that just opened?
Kelsey: I don't know; I heard their service isn't very good.              
Bill: Where did you hear that?
Kelsey: I read a review on Yelp.
Bill: Oh. Well, I take reviews on there with a grain of salt. A lot of people only write reviews if something went wrong and they want to complain.
Kelsey: True, and it got a pretty good review in the paper. Yeah, let's try it and decide for ourselves.


In this case, Bill says to take online reviews with a grain of salt, suggesting online reviews are often skewed. 

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Be On The Fence

Context #1

Jim:  Have you decided who you're going to vote for?

Chris: I still don't know.  I'm kind of on the fence right now.  Both candidates are qualified and seem great for the job.

Context #2

Carol:  Have you and your husband found a new apartment yet?

Shelly:  Well, we're still on the fence about which city to live in.  I want to live closer to the beach, but my husband wants to live closer to his work. 

MEANING: to be on the fence means that you cannot make up your mind between two choices or alternatives.  It means that you are having a hard time deciding on one thing over the other. 

To Wake Up On The Wrong Side Of The Bed

Context #1:

Tom: Man!  Chrissy must have woken up on the wrong side of the bed today!

Steve:  I know.  She is in such a bad mood.  

Tom: I think I'll just stay away from her today.

Context #2:

Sara:  Jenny, can I borrow a pen?  I forgot mine.

Jenny: Really? Again? You always forget your pen.  How many times has it been now? A million...

Sara: Wow!  Somebody woke up on the wrong side of the bed.

Jenny: I'm sorry.  Yeah, I'm a little stressed out today.  Here you go.  You can use this pen.

MEANING: to wake up on the wrong side of the bed is an expression used when someone is really grumpy or in a bad mood.  It is almost always used with a past tense form, like in example #2.

A Stone’s Throw

Example: 

Stephane:  I’m looking for the emergency clinic.  Someone told me it was pretty near.

Sean: It’s a stone’s throw away.  You see that building fifty feet away?

Stephane: The pink one?

Sean: That’s the one.  Just next door.

Stephane:  Wow, no kidding! It really is close.

Meaning: "A stone’s throw" means a very short distance; In other words, as far as someone can throw a stone.   Most people can’t throw something very far, so when this expression is used, it typically means you’re within sight of a location, thing, or person you’re looking for.

A Baker's Dozen (used as a noun)

First Example:

Stephanie: I need to get some bagels for a meeting.

Baker: How many do you need?      

Stephanie: Well, there's going to be 10 people, but I want a couple extra because I'm not sure what everyone likes. So I guess a dozen.

Baker: How about a baker's dozen, which is thirteen?

Stephanie: That's perfect!

Meaning: A "baker's dozen" is a phrase that really just means "13" of something. This expression is most commonly used when purchasing baked goods, such as bagels, donuts, rolls, etc. It refers to the tradition of a baker throwing in one extra when a customer purchases 12 of something, as in the example above.

Second Example (added by request):

Christina wanted to give out donuts during her class presentation. There 12 students including herself, but there was also the teacher, so she asked for a baker's dozen.

Origin (a little something extra):

It's commonly believed the expression comes from medieval England, when there were strict laws regarding bread sellers. Since bread was a staple in the people's diet, there were laws regulating the price of bread based on weight. So if a baker sold a customer a dozen loaves, but accidentally only included 11 loaves, or one of the loaves was under weight, that baker could be heavily fined for overcharging the customer. So bakers started throwing in an extra loaf for orders of a dozen loaves, just in case, and the expression was born.

To fall into your lap

Example 1:

Tom and Elizabeth are brother and sister. Tom has been looking for a job for about a month.

Elizabeth: How’s your job hunt going, Tom?

Tom: I finally have a job

Elizabeth: Really?

Tom: Yes! I’m going to be working as a Coder for Google.com

Elizabeth: Oh wow!! That’s so exciting! Congratulations

Tom: Thank you sis!

Elizabeth: How did you get that job?

Tom: I’d turned in my resume about two months ago and completely forgot about it. Well, they called me last week and interviewed me over the phone.

Elizabeth: That’s amazing! It seems like it just fell into your lap

Tom: Yes! I’m surprised how easily it fell into my lap. They want me to start tomorrow.

Elizabeth: I’m so happy for you

Tom: Me too.

Example 2:

I’ve been looking for a cheap apartment in West Hollywood. My best friend pays $950 for a one bedroom apartment there. That rate is unheard of for that area. She told me that she is going to be going to Russia to teach English for one year, so I can take over her lease. I’ll be paying the same amount for rent. I can’t believe how effortlessly that apartment fell into my lap.

Meaning: To come to you without you making any effort.

http://languagesystems.edu/