alt Hacker NewsRead "the terrifying art of finding customers" by Collin Stewart
Very few know more about outbound than he does, and that book is recent.
My two cents: It's unlikely you can make outbound work for a custom software dev studio unless you go extremely niche and have a way to target customers with relevant needs. The more broad your services the more new business depends on trust, and outbound has the lowest trust context of all top of funnel sources. What works best for dev shops is word of mouth.
Maybe consider a referral program.
Anything that can greatly boost trust when prospects learn about you.
Somehow, word of mouth never worked for me. I only ever got one repeat customer (he was really really good first time, but second time, mediocre), and one customer through a referral (very good, but just once). Out of 170+ over 25 years.
I see the reason: my customers are people who don't know anyone they could possibly recommend me to, because they are from random industries and random places. Also their projects are one-off: usually first and last software projects of theirs, ever. Working for someone with large networks who can make referrals means losing money because these people also know good coders and can hire well. I never solved this and rely on outbound all my life.