The hardest part for me was learning how to spot good clients from bad clients. Reading the "Win without pitching" manifesto"[1] transformed my business (I'm not affiliated in any way).

"Breaking the time barrier"[2] is also a good book I wish to have found earlier.

[1] https://www.winwithoutpitching.com/the-manifesto/

[2] https://www.freshbooks.com/fbstaticprod-uploads/public-websi...