1. Supply as PDF, all pages in single PDF
2. Ensure the PDF is set at the actual size, or if scaled, be sure to advise the scale (usually only for very large formats)
3. Everything in CMYK
4. At least 3mm bleed on each side
5. Cropmarks
6. Images at 300dpi
7. Fonts converted to curves/outlines or embedded
8. No essential information any closer to the edge than 3mm to allow for trimming variation

If you need spot gloss, special colours, foiling, embossing, debossing, folds, scores, die cuts etc, then you will need to get the specific setup instructions for your job. Please ask!