Items that are small/light enough to be in a typical cardboard box... pack it to survive being thrown off a 2-story roof landing on concrete, and you'll probably be ok. Double-boxing fragile items (e.g, €5k headlight lenses) is highly recommended.
Big, heavy stuff is more difficult: differentials, transmissions, engines. Building a wooden crate is the safest method, and don't skimp on the wood size.
Always include a duplicate shipping label inside the box or crate, with both addresses / phone numbers, in case the main external label is lost or damaged. If the label is lost, the shipper has no idea who the item belongs to, and it goes into a black hole for all eternity (likely sold at auction or scrapped).
As noted above, the insurance is basically worthless for damage (it's always the shipper's fault for inadequate packaging, even if they ran it over with a truck)... but if they completely lose the package, that's on them.
