Payment terms are often the least-read part of a client contract, and the part most likely to cause real problems later. A few things worth checking specifically before signing anything.
Net terms. "Net 30" means 30 days from invoice date, not from project completion, and some clients quietly run Net 60 or Net 90. Confirm the exact clock and where it starts.
Approval gates. Some contracts tie payment to internal client approval steps with no deadline attached, which can stretch indefinitely. Push for a fixed payment date regardless of approval status, or a clear approval deadline.
Kill fees and cancellation terms. Check what you're owed if the project is cancelled partway through, see the kill fee calculator for how to structure this if it's missing.
Late payment consequences. If the contract is silent on late fees, add your own before signing, see the late fees guide and the late payment fee calculator.
None of this is adversarial, it's just making sure the terms you're agreeing to are terms you can actually live with if things go slowly.