-ba yokatta ―ばよかった
When added to the stem of the dictionary form of a verb, expresses the speaker’s regret.
Example 1:
田中さんと相談すればよかった。
Tanaka-san to soodan sureba yokatta.
I should have consulted with Mr. Tanaka.
Example 2:
日本に来る前に日本語を勉強すればよかった。
Nihon ni kuru mae ni Nihongo o benkyoo sureba yokatta.
I should have studied Japanese before coming to Japan.