Create a real nomination. Don't just send a short email that says "I am out of time, he/she is obviously a star. Just look at these papers and awards in his CV." The nomination can just be a page or two, but it takes careful thought and effort to write a good one. Longer does not always mean better. We have seen weak but long nominations. We don't have a strict length limit, just use good judgement. It should be long enough to make the case clearly, but no longer :-)
Clearly identify the "body of work." Pointing at a bunch of papers is not good enough. Explain the significance of the work. Explain who cares about this work and who are the direct beneficiaries. Explain the context and origin, so we can understand why it is so influential. Just solving a long-standing problem is not enough. Explain why that problem matters and who really cares about its solution.
Don't recycle promotion digests with light editing (it shows). They serve a very different purpose.
Best papers are not ends in themselves. They may be good hints at Newell-Award-worthy work, but what counts ultimately is real-world impact. Which communities now do things differently because of this body of work? Which companies have now adopted the learnings from this body of work in products? Which group of people are directly using the output of this body of work (e.g., open source software or benchmarks or data sets)?
Citations are cheap. They are not strong evidence of impact. Doesn't hurt to have a lot of citations, but they are only mild evidence of impact.
Large number of published papers is not (by itself) a Newell-Award-worthy accomplishment.
Don't worry about trying to precisely quantify the accomplishment (e.g., via selectivity measures for all the conferences and journals in which those papers appeared). Just focus on the scientific substance and its impact on the world.