Depends on what the offering is, the most important thing is that you have the intent on giving that specific offering to that specific spirit.
Its your intent that guides the energy of the offering to that spirit. It is also important that you say that, that offering is only for that spirit and no other spirit. As it thought that any wandering spirit that is in the vicinity might swoop in and feed upon the offering.
When I offering incense I usually hold the sigil/seal of the spirit above the smoke. As a way to make extra sure the offering gets delivered.
Here is a thread that might be useful.