"Make sure your GETs are side-effect free. This is a biggie, the one where many services get it wrong. GETs must be both safe and idempotent. In turn, anything which does not have side effects should use GET.
So if you want to create a new resource, use POST. Want to retrieve a representation of a resource? Use GET. To update a current resource, use PUT. Finally, to delete a resource, use DELETE. "