This page is really N5 level grammar, but is a good example of verbs as adjectives.

ほうがいい

Better to do
Dictionary form Verb + ほうがいい

ほうがいい can also be modified by verbs, giving it a meaning of “it is better to do“. 

• 学校にいくより、家にいるほうがいい.  – Rather than go to school, being at home is better.
• 勉強するほうがいい – It’s better to study.
• 食べるほうがいいよ – It’s better to eat. (you’ll be hungry later)

You can make ほうがいい past tense by conjugating いい.

• 勉強するほうがよかった – It would have been better to study.
• 準備するほうがよかった – It would have been better to prepare. 

Past Tense + ほうがいい

Better to have done
Plain Past tense + ほうがいい

You may also use the plain past tense to modify ほうがいい, but this does not make the sentence past tense.
The past tense here is “Completion past tense” in other words “have done” “has been done“. 

Nuance wise, this phrase has a meaning closer to “should (best option should)“. 

• 傘を持ったほうがいいよ。- Having carried an umbrella would be good. (You should take an umbrella)
• 食べたほうがいい.  – Having eaten is good. (therefore you should eat)
• 見に行ったほうがいい – Having gone to take a look is good. (You should go take a look)

したほうがいい vs するほうがいい

Meaning wise, there’s barely a difference betweenしたほうがいい and するほうがいい.

• したほうがいい sounds more like advice.
• するほうがいい sounds more like the best option from choices, and is more neutral (objective)

This means when you want the nuance of “best/better” you should use するほうがいい;
and when you want the nuance of (you) should you should use したほうがいい

Source (Japanese)