Make a list of the essential things you need for your trip. Depending on the length of your trip, you may need to plan to do laundry at one of your stops. This cuts down on the amount of clothes you'll need to take.
Plan on packing light. Pack only what you can carry in your saddle bags.
Think travel-size. Small bars of soap and shampoo can be packed in a small plastic bag. Any convenience store carries items such as these if you need more.
Roll your clothes, don't fold them. You can roll jeans and a shirt together and slide them into your saddlebag easier than folded clothing.
Pack clothing, towels and bedding in the bottom of the saddlebags, then place toiletries and maps toward the top of your saddlebags.
Pack anything you don't want to get wet in plastic bags. If you're riding in the rain even stuff inside your saddlebags can get wet.
Weigh your saddle bags to make sure the weight is evenly distributed and doesn't go over the recommended weight for your motorcycle.
Use elastic cords to tie down your tent and sleeping bag. If you have a sissy bar, place these items ahead or behind it and attach them to it. They will ride more securely this way.
Place your rain gear somewhere on top, tied down with bungees. You don't want to have to unpack your bags in the rain to get to your rain gear.