Well, Hutch6390:
This is what I do, and most of the Lads think I have a couple lorries full of pebbles missing from the old head ya, know! I am at present working on over twelve models. Five in Card! Now when I feel the urge waning, I just move that one to the yard and pick up where I left off on the one I have chosen.
No, There actually no confusion as to where I stopped. I mark the model in a spot that won't be seen, to indicate what step I was at and the instructions as well. Then I just pick up there.
This isn't that hard, because I may get a stray thought or ping an Idea from an ad or another modeler and try it on the model that I set back cause maybe it got Boooooring! Yes, Modeling can get you to a stage that the steps seem so rote it gets Boring-Time to change.
This is why I have so much going on at one time. About the only variance from that is when I am scratchbuilding a ship from plastic. Then I plan the Ship, It's Layout, Deck Hardware and Scale and ERA. Then I gather the material together I know I will need.
Then I transfer the drawings to the plastic and start the ship.