Last year I bought some packing cubes for traveling. What a difference they made. I got them on Amazon - variety of sizes actually, and I found them to be even more useful than I was thinking. They helped me fit everything into the suitcase neat and clean. Makes it very easy to unpack as well (and still keep stuff in the suitcase, since everything is organized).
Of course, I start making a list 1 week if traveling overseas, or at least a couple of days for domestic. That way I always remember a thing or two to add to that list and when it's time to execute - my marker goes fast from the first to.. gazillion-th point. :)
Planning outfit is another page in my diary - I go as far as I take pictures with my camera and matching outfits (yes, my family laughs at me for doing that, but then… when comes the time to execute fast out-door outfit - abra-cadabra and I'm done!).