Short papers develop incisive writing. Long papers often ramble. Require a short paper. The introduction is a key source of procrastination and should be written last. Ideas evolve with writing.
Writing is a thinking tool.
Introductions and conclusions also evolve and should be written last to save time and frustration. A reader presented with data and no explanation or development will nearly always reach a conclusion different than the writers. Lead the reader through the data to the point. Every paragraph should have a clear transition that looks back to the previous paragraph and forward to the coming idea. This sentence, if crafted carefully, should also look to the position so that the thread of the argument and the idea are clear.