Grammar JLPT Level N4 - Lesson 30

Structure of ば良(よ)かった:

Verb［ば］+ よかった

Examples:
食(た)べる￫食(た)べれば + よかった
飲(の)む￫飲(の)めば + よかった
する￫すれば + よかった

Details about ば良(よ)かった:

ばよかった is a common expression used when someone regrets that something has not been/was not done. It is a pairing of the conjunction particle ば, and the past form of the い-Adjective, 良(い)い (remembering that conjugations of いい use よ, and not い). This construction is often translated to 'I wish I did (A)', or 'I should have done (A)'.
ばよかった is used after verbs, so requires the standard ば conjugation, before adding よかった.

サービスエリアが一(ひと)つもないじゃないか。高速(こうそく)に乗(の)る前(まえ)にトイレに行(い)けばよかった。
There aren't any service stops, are there? I wish I had gone to the bathroom before we got on the highway.
今日(きょう)も残業(ざんぎょう)？昨日(きのう)は早(はや)く寝(ね)ればよかった。
I have to work overtime again today? I should have gone to sleep early last night.

As ば highlights hypothetical situations, ばよかった literally means that 'it would have been good if (A)', where (A) is the thing that the speaker wishes had happened.

ば良(よ)かった