Conversion projects often begin with the landing page and stop before reaching the form. That is the wrong order, because form friction is cheap to fix and its effect is immediate.
Count the fields, then justify each one
Every field should earn its place by changing how you respond. If a piece of information does not change your reply, ask for it in the reply instead of on the form.
Fix the error messages
Errors should say what went wrong and how to fix it, appear next to the field in question, and never clear what the person already typed. A form that discards a long message because of a formatting problem loses that lead permanently.
Confirm that submissions arrive
Test the form monthly and store submissions in the site as well as emailing them. Silent form failure is the most expensive bug a website can have, and it is often discovered weeks late.
Say what happens next
A confirmation that states when someone will reply, and who from, reduces duplicate submissions and sets an expectation you can meet. It costs nothing and it improves the first impression of working with you.