Beautiful is used when you describe something or someone.
Ex: 彼女は、とても綺麗だ。
This girl is beautiful.
OR
Ex: 風景が綺麗です。
The landscape is beautiful.

Lovely can also be used to describe something or someone (more similar to かわいい). Something that is cute, pretty.

BUT "lovely" can also be used to describe someone's behavior.
例状況: 友達はあなたのコーヒーを買います。
Your friend buy you a coffee.
In this situation you can say to your friend: "thank you! You are so lovely!".
"Lovely" because your friend did something nice for you. :))

I hope it helps :)) がんばってね‼︎（＾ω＾）

@darica Do you also say "You are so sweet." when someon did something nice for you?

* @Darica

@stbnzi: well basically whether you say "it's a lovely scenery" or "it's a beautiful scenery", it's the same meaning. But the word "beautiful" emphasizes the beauty of what you see. The term "beautiful" is stronger than "lovely". :)) but you can of course use both ^^ lovely is similar to pretty, when beautiful is more like ~ 美しい

@sallykyoko: yes it's also correct!! You can also say "sweet" when someone does something nice for you ^^

I got it @Darica ! Thanks so much!

どういたしまして
（＾ω＾）

My pleasure :)