An auto-clicker is suggested.

There is a hidden boost that is activated by clicking the monster girl. All math is explained in the bottom section.

Originally posted by Devs:

Touching them will boost your production rate and affect your favorability rating.
Depending on where you touch, boost rate and fluctuation of favorability rating will vary.
By reaching maximum favorability rating, Monster Girls will start off Support Mode, which further boosts your production rate.

By clicking on their head you can fill up the heart bar, and while clicking on their head, this grants a small boost in production speed and you'll see the bars of each unit increasing faster.

When the heart at the bottom right on the monster girl is fully increased a small scene will play and you'll enter Support Mode, you'll get a value boost to each unit and their character pane will turn a pink colour.




While the character pane is a pink colour you are able to click on the monster girls chest and crotch area and you'll get a bigger boost in production speed than you would if just clicking on their head.
There is a 3 minute / 180 second cooldown on the ability from each monster girl and during this time you are only able to get the boost in production speed as if the heart hadn't been filled at all. You are able to move to the monster girls chest and crotch area during this time, but you'll decrease the heart meter and run the risk of getting a production debuff.

As can be seen from the above table, leaving an auto clicker on the Monster Girls head will yield a 50% boost to production (150%) and every three minutes when you get the heart buff you'll reach a 125% boost (225%) for 20 seconds.

If active clicking, you can rotate between head and chest to get the most out of the boosts, and click the chest during the heart buff where your heart meter won't decrease.
There is probably an AHK script that can manage this if someone wants to write a clicker script that targets the head and rotates accordingly when the buffs land.

When you summon a new Monster Girl all your units will automatically level up, this gives all your units a permanent 50% boost to their production.