Here's the important things to take in consideration to start effectively.
I'll not talk about the technical part, clean list, dns records....
First you need an offer that is in demand and solves a real business problem.
Don't send generic emails, you need yo sound like it's personal, use personalization and Ice breakers,
Don't send fancy html, keep it very simple. It's like writing a personal message to a CEO of another company.
Quick example: Hi {Firstname}, I just saw your post on LinkedIn about {topic} I'm really impressed about what.........We just helped {XYZ competitor company} to achieve.....
If you already worked with some clients, show what you already did, if you don't have any client yet, work for free for some clients and get them results then use what you did in your marketing