We went slowly at that point as well.
First day, we used base 10 blocks. We'd work the problem with the blocks, then we'd redo the problem with the blocks while I wrote the notation for each step. I really liked using the base 10 blocks because you see WHY you go from large to small when all the other operations go from small to large.
Second day I had my son write the work after using the blocks.
As we kept going, I'd have him use the blocks any time he got a problem incorrect using math notation.
I know mnemonics can be helpful, but I've got concerns using them for arithmetic operations. I tend to see where people run into problems with mnemonics though, so that colors my dislike of them. I really liked the base 10 blocks and going from concrete to abstract.