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 接続助詞（せつぞくじょし） (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.