You may think, "not this old Singer, it's indestructible!" but the fact that it is so heavy and sturdy also makes it vulnerable when shipping. It can bust out of its confines, becoming susceptible to dings, dents crack and worse. I'm displaying a 1956 Singer 301 and a ton of accessories for this demo, but you can modify to suit any machine, obviously. Just note your trouble areas and deal with them accordingly.
Okay, here we go!
Step 1: Gather your materials.
1] Good strong packing tape
2] Bubble wrap, about 20 feet.
--- Usually it's $2.99 for a roll at USPS or Kinkos. I am not sure how long a roll is, so you may have to spend up to $6 if you don't have any around.
3] Styrofoam peanuts, one large box full (probably four crappy plastic shopping bags full.
--- I don't know anyone who doesn't have a bag or box in their garage, so if you happen to be one of those rare creatures who does not, chances are at least one of your friends does. If all else fails, ask on craigslist! You can also use slabs of styrofoam for this but it just has to fill in all gaps and be snug!
4] Two sturdy shipping boxes. The first (or inner) box should be about 4-5 inches larger than the sewing machine on all sides. The other (outer) box should be about 4-5 inches larger than the first one on all sides. This is a general thing. The idea is that the machine will have ample padding and will not move AT ALL within its box. This may be how the average person would think it was safe to ship. BUT that box then needs to be surrounded on all sides bu additional padding in an outer box.
NOTE: You can use blankets and pillows etc instead of bubble wrap and styrofoam and it would probably get there safely, but it would also double your shipping fees so it's really cheaper to buy the packing supplies if you have to.
Step 2: Deal with "problem areas" first.
In some models (the 221 Featherweights especially) it is recommended that you actually remove the entire bobbin winder as it is most likely to break off in transit.
In many models it is safer to remove the presser foot before shipping.
If there is a carry handle, make sure it is folded in.
Flip up folding bed (if there is one) and add padding where needed.
Basically, get the machine as small and compact as it will go. This may mean removing a few extremities. Again, in the 221 you will also want to remove the top that holds the thread spool.