ばようかったです means I wish I had done or I should have done something. You can use it to describe an alternative course of action you, to your regret, did not take.
I wish I had told her that I loved her.
All verbs can regularly be turned into a ばよかったです sentence with no exception or irregularity. YOu form the ば-form on the basis of the present tense short forms.
Verbs in the affermative:
Drop the う and add: えば: たべる -> たべれば
Verbs in the negative:
Drop the final い and add ければ: たべる -> たべなければ