It depends on where you're starting. I'd start with New Sales Simplified by Mike Weinberg. It's a great primer that teaches what's "possible" in places like this.

Then, I'd really try to get with client selection and balance activities between Salmon and Whales.

You want to find people that can grow, are in healthy categories, and that may take more effort to get the initial sale, but will have bigger opportunities once you're there.