How to say “If you're going to Japan, you should buy a train ticket before you leave.” in Japanese

In Japanese

日本(にほん)に行(い)くなら、出発前(しゅっぱつまえ)に電車(でんしゃ)の切符(きっぷ)を買(か)っておくといいですよ。

Nihon ni iku nara、shuppatsu mae ni densha no kippu o katte oku to ii desu yo。