Pending on the size of the item really.....
But here's a few ideas that I use.........
I perfer to leave motors as complete and sealed up best as posiable
engine heads I store on their ends and wrap em up in shrinkwrap with a small amount of "kitty litter" sprinkled in as I wrap em up.
engine blocks I leave the sumps on if possiable and then fit a sheet of perspex over the head face of the block, usually sealed with silicon ( non acid type). Dump the oil first tho and chuck a good handfull of kitty litter into the dry sump before refitting it.
same procedure for gearboxes, diffs.... leave complete if posiable
Its the individual parts that used to cause the grief ......
Things like.... gearbox gears/shafts/, camshafts, rocker gear, cranks, diff centres, CV's, etc etc
For the larger of these items I spray em with "chainsaw bar oil" and then wrap em in shrinkwrap or "grease proof paper" ( see the missus' kitchen draw with the gladwrap in it

)
Run the Bar oil through a "kero washer "...heat it if it wont spray by sitting the pot in some hot water.
The smaller items that can be easily lost or damaged by longterm storage I have come up with a kewl system that works really well....
I use 25 litre drums that I get from the local fish n chip shop for free....
( the ones that the cooking oil comes in. )
chuck the parts in and fill em up with diesel to just cover the parts.
The lids seal up really well and are just about air tight
They can be stacked one on top of the other
Texta will be easilly seen on either the top lid or sides of the drums
The drums are 100% reusable
The diesel in a couple of the drums I have is 15 years old and still good!
They have a sturdy carry handle
ideal for engine internal parts ... pistons with rods still attached etc
another tip.....
stack em around 4 high and every few months give the stack a little bit of a nudge....this will help "stir the diesel" and therefore wash the parts too

while recoating any "dry areas""
yet another tip....
seized parts / tools left for around 12 months will be a lot easier to pull apart.
and the final tip ....
Its a great way of using that contaminated diesel up ! ( not the water contaminated stuff )
and if diesel is too dear to buy then mix it with sump oil
( around 50 / 50 mix )
I have 2 drums that have some "special parts" in em and these drums have paint thinners instead of diesel. The evaporative loss is nill over 4 years so far
Last count there was around 20 odd drums of parts stored this way.....
and counting ...... one of these days the loft will come crashing down
Kingy