The clauses not to forget
A solid contract spells out: the parties and their details, the exact deliverables (number of pieces, platforms, formats, publication dates), the price and payment terms (deposit, timeline), the usage rights granted (can the brand reuse your content, where, for how long), any exclusivity (are you turning down competitors, and for how long), the advertising disclosure, and the terms for changes or cancellation.
The usage rights clause is the most underestimated of the lot: "post it on my account" and "reuse it in paid advertising for a year" are not the same product. Separate them clearly and price accordingly.