Written by Henrik Bondtofte, who has been building links since before it had a name.
Most link profiles I look at fail in the same five places. None of them need an agency to fix. They just need someone to notice them.
Directories have a bad name from 2011, when people fired off a thousand submissions over a weekend. Used with your head, they are still the easiest place to start.
You do not need an agency to start building links. You need a list, a rhythm you can keep, and enough patience not to ruin it for yourself in week two.