Some things I learned through mistakes:
- Charge more.
- Travel like a professional and bill the client. For my first business trip I used airline points, stayed at an Airbnb on my own dime, and even refused the client's offer to reimburse me. Stupid. (Full story here: https://www.gkogan.co/blog/stupid/)
- If I'm not enjoying the work, request a change or move on. Don't just "tolerate" it and chug along. One of the greatest benefits of consulting is the freedom to chose whom you work with... Take advantage of it.
- Remember who the client is, and don't get too involved with their subordinates.
- If you don't feel "Hell yes!" about taking on a project or prospect, just skip it. It's not going to get more interesting over time.
- Find a great accountant. Fire bad accountants fast (and lawyers, and other service providers).
- Tell the client the hard truth.
- Impostor syndrome is normal. Get over it.
- Stop trying to go above-and-beyond all the time. Do what you were brought in to do, and do it exceptionally well. If other opportunities come up, suggest them as follow-on projects instead of just doing extra stuff for free.
- If you're clashing with an exec at the company, tell the client, instead of just backing away from the project.
- There are hundreds/thousands (depending on specialty) of potential clients out there, you just have to find them. So don't worry if a deal falls through, don't envy other consultants, and don't take on bad projects out of desperation.