Store items you need most at front of unit. Create a center aisle for access to all items and the back of your unit. Place heavy items on bottom, lighter on top.
Resist the temptation to use garbage bags for storing items. Wardrobe boxes work best for clothes. Use the same size boxes, when possible, for increased stackability. Keep boxes less than 30 lbs., correctly labeled, with lids closed and taped.
Time spent on this now will save you considerable time and effort later.
Allow a small amount of space along the walls for ventilation. Leave appliance doors ajar to prevent odor buildup.
Some sofas may be placed on end. Break down furniture when possible keeping parts together. Place chairs seat to seat. Stack, stack, stack using all vertical height.
Mattress and sofa covers will protect your sofa and mattress from dirt and dust. Mover's wrap is great for protecting all your belongings.
Use lots of paper and packing material for glassware, etc. Lamps are also delicate items and shades should be boxed for protection.
Old photos tend to curl over time so use cardboard taped together to keep flat. Books should be stored flat to protect their spines. Boxes will be heavy so pack in smaller boxes.
Drain gas/oil from lawnmowers or small engines. Wipe down metal with a rag containing a few drops of machine oil to resist rust.
Allow sufficient time to do your job well. Remember to keep hydrated!