Six steps, in this order
Who you are. Brand or agency, and which brand the campaign is for.
The campaign. What is being promoted, to whom, where the traffic comes from and the number that decides whether it worked.
The mechanic. What a visitor actually does, what they walk away with, and the logic behind the result. This step moves the price more than any other.
Data, systems and the legal bit. What you collect, where the leads land, which countries it runs in, who writes the terms.
Content and languages. Who supplies the text and the product data, and in how many languages it has to run.
Dates and the rest. Launch, end, what happens to the page afterwards.