Moves that involve shorter distances are usually the hardest because you don't treat it the same as you do for a longer move. You thin why bother to pack it, I'll just carry it over. More trips = more fatigue. We have moved numerous times for my husband's job and now I've been helping my kids move.
1. As you pack things into boxes for the move, sort and toss. Why move expired meds or foods?
2. The first things to pack are the things you need the least. Put them in a box, labeled and move them to the final destination room. You can deal with opening them later, as needed.
3. The critical rooms are the kitchen, bathroom and bedroom. If you won't need it in the next 10 days pack it now. The last things you pack are the first things you need - sheets for your bed, towels & toiletries, the coffe pot.
4. It is worth it to line the shelves with liner before you move in (kitchen, bath, linen closet). Put sticky notes on each cabinet & drawer listing exactly what you plan to put in it. If someone wants to help, they can unpack & put away items the way you want them. (That's my job when moving the kids - not intrusive, but very helpful)
5. You can carry the drawers from your furniture over without emptying them (taking the drawers out lightens the furniture), but clean them out before moving (lighten the load and keep the new place clean).
6. Keep a tool kit available - screwdrivers, hammer, pliers, tape, nails) and the cleaning supplies out for touchups.
7. Plan on takeout meals. Let your sister pick the food. And breakfast the first morning in the new place should be out - less pressure to have the kitchen ready to go.
8. As soon as you get the bed moved, make it so it is ready for the end of the day.
9. Your cat/cats need to be confined to a room or a large closet (preferably in the old place so it is familar) while you are going back and forth between appartments. Put a sign on the door as a reminder not to open unless the doors are closed - sounds dumb, but when you get tired..... And in case you suddenly get extra help, they are protected.
Good luck, have fun.