also: おけばよい
expression, i-adjective (yoi/ii class)
it's OK to ...; it's best to ...; it's alright to ...
Used after the て-form of a verb to express that doing that action is acceptable, advisable, or the right thing to do. The note indicates it is usually used as verb-て...
もう帰っておけばいいよ。
It's OK to go home now.
わからないことは先生に聞いておけばいい。
If you don't understand something, it's best to ask the teacher.
Similar pattern using する (to do) instead of 置く; 置けばいい specifically uses the verb 置く (to put/place) in its conditional form, often implying leaving something as is or taking a preparatory action.
Formed from the conditional form of 置く (おく, 'to put/place') + いい/よい ('good'). The expression grammaticalized from the literal meaning 'if you put it, it's good' to a general pattern meaning 'it's good to do something (in advance/preparation).'