Which metric do you focus on: input, output or outcome?

Youtube: Don't count subscribers but videos published!
Twitter: Don't count followers but tweets published!
Email: Don't count subscribers but... oh no.. every time we send an email we loose 20 subs!

Try to focus on the metric that is most correlated to the value of your product/service.
Your customer is more likely to happily pay more, if that will give them more value.

I can strongly recommend episode #120 of the indie hacker's podcast with Patrick Campbell of ProfitWell (helping companies to price better). He speaks really clearly and thoroughly about the nuances of pricing.

When Stephan King finishes a book, he starts the next one the day after. Don't stop!