If I could get the most out of cliches, I would say that it depends on the type of paper.
But, there are better answers to this, and I cannot articulate clearly an effective way, but surely I can say what we should be looked for: the effect of the start of the paper; a good paper starts with the overall "atmospheric" of consciousness at the moment the paper is set to be written that entails the overall understanding of the subject matter (which does not mean Absolute Understanding)--it is when the writer shows that he catches the TEMPO of the writing (or the beat, the pulse), when he and the text in front of him are intertwined (Merleau-Ponty calls this the "chiasm"), when the text speaks as the writer speaks, when the writer continues to speak even when the text ceases. This should be done in the first three sentences--it could be less, but no more, maybe: use long sentences if needed, be concise, "in and out", sort of--because the reader does not have a lot of time at his dispense, be textual, and even more: be contextual, start from the notion of multiplicity before actually introducing anything. If one could, one should stay forever in the multitude of interpretation, and be sure that the reader would be able to keep up; which is to say, produce a scriptible text (writerly text) and not a lisible text (readerly text)--produce a piece of writing that others could pick up and continue the conversation immediately as if the writing bleeds out of the page itself.
Note: I did that in 5 sentences, which is not up to the standard at all.
Here are examples:
"On Truth and Lies in an extra-moral Sense"
Once upon a time, in some out of the way corner of that universe which is dispersed into numberless twinkling solar systems, there was a star upon which clever beasts invented knowing. That was the most arrogant and mendacious minute of "world history," but nevertheless, it was only a minute. After nature had drawn a few breaths, the star cooled and congealed, and the clever beasts had to die.
"The Pleasure of the Text" (Le Plaisir du Texte)
Section on Voice
If it were possible to imagine an aesthetic of textual pleasure, it will have to include: writing aloud. This vocal writing (which is nothing like speech) is not practiced, but is doubtless what Artaud recommended and what Sollers is demanding. Let us talk about it as though it existed.