You should assume:
There is no fragile service (because they use machinery) its just marketing on your part so the receiver thinks you done well.
It will probably get treated well when received and when passed out to the addressee. However in the journey between; the parcel will be dealt with by many different people/ machinery who do not deal with the general public.
That the parcel will be dropped from chest height as parcel are sorted by machinery/rushed humans/ chest height parcel trolleys.
That other people will not package their packages well and this could impact yours. ie your bubble wrapped item hitting another bubble wrapped item equals better protection.
That you want your package to sit in the bag with the lighter parcels not the heavy ones.
That being on the top of the parcel bag is bad if there is a heavy packages on the bottom.
That parcels will be thrown. Put fragile labels in clear writing near the To address so that sorters cannot not miss the text ... they are sorting many parcels.
However do not put so much text on the box that it impedes the sorting process.
That having the parcel not sitting in a bag and separated may or maynot be a good thing. A bag may more often be carried and dragged over to the next spot while an individual parcel will either be picked up and carried or picked up and thrown.
Figure out when the collection of mail occurs at your local office.
Know your posties and mail contractors and tell them you are expecting eggs/sending eggs.
Cover up address labels on reused boxes otherwise mail could go for a trip.
Do not write the to address on the from section of the box and then scribble it out and write "To" ... it will come back to the same office and they will keep reposting it back in the system. Make sure you have the correct post code on your package.
With post office Do not put two addresses on the one package.. One package can only go to one address. {So send two packages

} (unless you post it with a different way such as a courier company and they request that you give two addresses). ...also postal address and street address can have different post codes as well.
Do not deviate from the addressing standard of your local country. ie
name of person
street address
SUBURB STATE POSTCODE
Versus
name of person street address suburb state postcode {written on the same line and not in the usual address spot}
This makes it harder to sort out.
Keep your hand writing as neat as possible. Do not use running writing.
Do not insult the post person by asking for stationery that isnt paid for ie tape; as about 100 other people will ask for tape because they have 18 year old vintage envelopes. Postage rates probably only covers the cost of the postage. The tape behind the counter is for the New boxes from their shelves. If you take boxes from the dumpbin outside that has been flattened and rock up to the post office expecting free tape ...
Fill your boxes to the top with filling. Shaking results in breaking boxes/ envelopes.