The essentials. How you will be paid, where, when how much. Who is responsible for what, when and where And for me the single most important part of any contract is default recourse, and the wording therein. I want to know that if the individual I contract with will be responsible to pay reasonable attorney fees should I be forced to sue to enforce the covenants of the contract we both sign. The recourse is a two way street, you default, be prepared to suffer being sued.
Secondly important for me is signatures, witnesses and having the document recorded for public actual notice.
Lastly, I hate arbitration and arbiters. It will likely be in the contract and you should not sweat if it is or isn’t. Just make sure the default recourse is in there, don’t sign without. If you can't punish the party to a contract, what reason does he/she have be prudent.