Most sales mistakes are habits, and habits can be changed one at a time. These are the ones that come up most often.
Talking more than listening
It feels natural to explain everything you know. But people decide based on their own needs, and you learn those only by listening. The fix: ask a question and wait, even when the silence feels long.
Giving up after the first no
A first no often means "not now" or "I do not understand yet". Ask what is behind it. Sometimes it is a real no, and that is fine. Often it is a question you have not answered yet.
Promising too much
To win a sale it is tempting to promise results. Promises you cannot keep cost trust, and trust is hard to win back. Say what is realistic and let the result speak later.
No clear next step
Many conversations end with "let's stay in touch", and then nothing happens. End every conversation with one agreed step and a date.
Explaining it the same way to everyone
People are different. Some want details, some want the big picture, some want to know who else uses it. Watch, ask, and change how you explain.
Doing it alone
Selling is easier with support. Talk through hard conversations with a colleague or a mentor. Most mistakes are easier to see from the outside.