The particle よ (YO) is used to give more weight to what is said, encourage someone to do something, emphasize a request.
一緒に歌いましょうよ。
Isshoni utaimashou yo.
Let’s sing together.
明日の会議に遅れないでくださいよ。
Ashita no kaigi ni okurenaide kudasai yo.
Please don’t be late for the meeting tomorrow.
2.
The particle よ (YO) expresses certainty and self-confidence. If the speaker disagrees with what someone else said, he/she uses よ to denote confidence in his/her own opinion.
明後日は祝日だから病院は休みですよ。
Asatte wa shukujitsu da kara byouin wa yasumi desu yo.
The hospital will be closed the day after tomorrow due to the holiday. (even if you think the opposite)
3.
よ (YO) can be used to express annoyance, or even anger.
君の服は派手すぎるよ!
Kimi no fuku wa hadesugiru yo!
Your clothes are too flashy!
喧嘩しちゃだめだよ!
Kenka shicha dame da yo!
Don’t fight! (to kids)
4.
よ (YO) is used to give your interlocutor a piece of information that he/she doesn't have. The speaker believes that the information is important.
事故に遭ったよ!
Jiko ni atta yo!
I’ve had an accident!
5.
よ (YO) can be used to draw someone's attention to an idea that you want to convey. Therefore, it is normal to find it more often in a conversation.
In some situations, this usage may upset your interlocutor if you don't use it correctly. In fact, it's important to understand that by using it, you put yourself forward. Avoid using it with your boss, for example.