Japanese - Telling you've decided on something with にする

You can use the phrase に　する to tell that you have decided on something.

I've decided to take the bus for this trip.	この　旅りょ行こう　は　バス　に　する。kono ryokou wa basu ni suru.
I've decided on a red dress for the party.	パーティー　は　赤あかい　ドレス　に　します。paatii wa akai doresu ni shimasu.

This phrase is also often used in restaurant setting.

What have you decided on? / What will you have?	何なん　に　します　か。nan ni shimasu ka.
Decision: I'll have coffee.	コーヒー　に　する。koohii ni suru.

You can also use に　しましょう to propose a decision.

Decision: Let's go with ice cream for dessert.	デザート　は　アイスクリーム　に　しましょう。dezaato wa aisukuriimu ni shimashou.
Let's decide on having a picnic on the day off.	休やすみ　の　日ひ　に　ピクニック　に　しましょう。yasumi no hi ni pikunikku ni shimashou.
Decision: Let's set today's meeting for 30 minutes.	今きょ日う　の　ミーティング　は　三さん十じゅっ分ぷん　に　しましょう。kyou no miitingu wa sanjuppun ni shimashou.

You can use にする after verbs by nominalizing the verb with the suffix 〜こと.

I've decided to travel abroad this summer.	この　夏なつ、　海かい外がい旅りょ行こう　を　すること　に　する。kono natsu, kaigairyokou o surukoto ni suru.
I've decided not to eat sweets anymore.	もう　お菓か子し　を　食たべないこと　に　する。mou okashi o tabenaikoto ni suru.

Japanese 328 - Telling you've decided on something with にする