I've travelled quite a bit since PMR - USA, Oz, S Korea, Japan, all over Europe.
Basic rules: even if it costs a bit more do NOT travel to the airport, check in, fly to destination, get to place you are staying without having every rest opportunity you can insert. Travel to the airport the day before if it is a morning flight and more than an hour or so drive. If it is public transport - spread it out even more. DON'T schedule short transfers - if it looks a rush, change the arrangements if possible, or ask the airport for assistance, even if you feel it's OTT. There is nothing worse than trying to run for a plane connection!
Allow at least one day after the flight across the pond to recover - land, go to a hotel close by and REST. Do not arrange something you can't rest on or not do for the next day. For example, I flew to S Korea, got to the hotel and had to have dinner with the hosts at the University guesthouse - I nearly fell asleep in my soup and felt physically sick I was so knackered. But I went straight to bed then and slept for 12 hours, got up, took the taxi to the train to travel across Korea and promptly went back to sleep in my seat. At the other end I went straight to our room - and went to sleep again. David went out for a walk - it rained so my choice was good! But then I got up and went for dinner feeling great, slept again and was up for the entire 3 days tour we did. I have to confess there were a few more steps at the temples than was good for me but I managed it fine.
Consider: could I do this at home? If you couldn't - how can I adapt/avoid it. Never plan to do two "busy" things on consecutive days - if you feel fine you can add something in on the free day but don't make it so you MUST do it.
DON'T try to reduce dose while you are away or in the few weeks before. If you are well at a dose 6 weeks prior to travel - stay there. I take a slightly higher dose the day before I travel, not very much but it helps - especially for the "long day". I don't fiddle with times and doses otherwise.
Are you Americanised or still basically a European? Think hard about museums and queueing and walking and heat and standing and waiting and... You get my drift! A gentle wander around a European city, from cafe to Biergarden to cafe, is one thing. Following a tour guide as they race from tourist attraction to tourist attraction is another! Is Venice on the menu? Walking in Venice is something else - 50 yards max before you go up and down steps in the form of a bridge over a canal, rinse and repeat. And the cafes cost a BOMB!
But you will have a whale of a time and it will be fun - as long as you allow for rest! As tavidu says look forward to it and you will have a great tim even if you don't do the Louvre, the Uffici or any of the other "essentials". The Louvre was fine for me in half a day, the Mona Lisa is greatly overrated. I still haven't been to the Uffici! There is a replica David on the piazza outside - opposite a cafe!