In contrast to
ばよかった, which is used for expressing regret about something that someone wishes had been done,
ばいい highlights that the speaker is hoping for a particular result, in relation to something that has not happened yet. This translates as ‘It’d be good if (A)’.
To use ばいい, add the 接続助詞（せつぞくじょし） (conjunction particle) ば, to the end of any verb, and then attach the
い-Adjective,
いい.
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どれを食（た）べればいいか迷（まよ）ってるところ。
About which would be good to eat, I am currently a bit lost.
行（い）ければいいけど、行（い）けるか分（わ）からない。
It would be good if I could go, but I don't know if I can.
Although
ばいい literally means ‘if (A), it’s good’, it can also be used to give advice, and has a meaning that is similar to ‘should (A)’ in these situations. It is generally quite a soft way of giving advice.
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テストでいい点（てん）を取（と）りたかったら、勉強（べんきょう）すればいいんじゃない？
If you want a good grade on your test, shouldn't you just study?
そんなに疲（つか）れているなら、仕事（しごと）を休（やす）めばいい。
If you are that tired, you should just take a day off.
ばいい may also be used when making statements about something that the speaker believes is not possible. In these cases, it is regularly paired with
のに, and has the nuance of ‘despite it being good if it were (A)’. This shows that the speaker thinks that (A) would be good, but is aware that (A) cannot/will not happen for some reason.
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明日（あした）早（はや）く起（お）きればいいのに、全然（ぜんぜん）寝（ね）れない。
Even though I want to wake up early tomorrow, I can't sleep at all.
好（す）きなら彼（かれ）にそう言（い）えばいいのに。
Even though you should just say it if you like him… (Why don’t you)
休（やす）めばいいのに、皆（みんな）真面目（まじめ）だから休（やす）まない。
They should take a break, but because they are all very diligent, they won’t.