Preparation and Trying

ておく

To prep
Transitive verb て form +おく

The ～ておく means “To do in advance/leave in a state for some purpose”. There is an intent behind the action. 

Examples

• ドアを開けておく – I’ll leave the door open (for some reason). 
• 彼に聞いておく – I’ll ask him (for advice, just in case, in advance of X)
• ほぞんしておこう – Let’s save this (just in case). 
• じゅんびしておいた – I prepared (it) in advance.
• パンを買っておいた – I bought some bread (in advance).

てみる

Try and see what happens
Transitive verb て form + みる

てみる could literally be read as “do x and see”. It is used to express “Try X and see”. It is most commonly used after receiving advice from someone else; or when going to do something you aren’t sure of. Because you are doing an action to see the result, it’s meaning is closer to test.  

Examples

• やってみる – I’ll go try it (and see what happens)
• 食べてみる – I’ll eat it (and see if I like it)
• 彼に聞いてみたが、知らなかった – I tried asking him, but he didn’t know.

Advice

てみる can also be used when giving advice:

• A: ねむたい – I’m sleepy
  B: コーヒーを飲んでみたら？- Why don’t you try drinking some coffee?
  A: じゃあ、飲んでみる – Ok then, I’ll try some coffee.

See also たら

てよかった

I’m glad that～
Verb てform + よかった

てよかった is just the ていい we covered in N5, but in the past tense. It means “It was good I did x”. This statement can only be used about the past tense, but the feeling is present tense.

Examples

• 勉強してよかった – I am glad I studied
• 合格して本当によかった – I’m really glad I passed.
• あけておいてよかった – I’m glad I opened the door in advance. 

It can also be used with intransitive verbs:

• 終わってよかった – I’m glad its over. 
• 開いていてよかった – I’m glad the door was open.