Compose your document in Word or another word processing or page layout program.
Reduce the size of photos and graphics before you insert them into your document. (Save the originals, though; if you’re a winner, DSNY may ask for hi-res versions.)
Proofread and spellcheck your document before saving as a pdf.
Use further compression when you save the document as a PDF.
The online submission form cannot accept PDF files larger than 3 mb. One of the biggest challenges can be keeping your file size within that limit. These online resources may be helpful: