1. Opt for a cheaper flight with a terrible schedule.
Speaking as a professional cheapskate, I totally understand the desire to save a few bucks, especially on something as un-sexy as airfare. There are just some people you really hate giving your hard-earned money to: bankers, dentists, Comcast, and, of course, airlines. That said, any joy you feel from depriving the airline from wrenching a few more bucks out of you will dissipate the minute you realize you are stuck for an 8 hour layover in JFK airport, wondering why half the ladies' room toilets are covered in black garbage bags, how a day old bagel can possibly cost $5, and how many martinis you can handle (and afford) before you catch the attention of airport security. Your time is a commodity and you need to think about it like that. If you save the money on airfare but arrive at your destination filthy, frustrated and exhausted, your first day will be a nightmare.
2. Pack too much stuff.
Pack your bag so that it is never more than 3/4 full, including an extra empty duffel bag in the bottom and a lot of bubble wrap. This will inevitably mean a drastic cutdown on clothing, shoes, books and toiletries. You can buy cheap shampoo, soap and other toiletries abroad, which gives you a chance to try something new anyway. This will also enable you to not check a bag on the flight over, which means you won't have to wait for your luggage with the rest of the schmoes and you can get out of the airport in less than an hour. Opt for magazines instead of books -- you can lighten the load by recycling them as you finish reading them. Plan to fill your bag with cheese, oil, beans, liqueurs, wine, grappa, honey, and jams. On the flight back home you can check a bag for free, and your bottles will be safely tucked inside the bubble wrap you packed. You can take the duffel as a carry on and fill it with your extra clothes, plus breakable non-liquids you bought on your trip. There is no beauty product in the world that is worth having for 7 days at the expense of bringing home a great bottle of walnut liqueur. Sure, some people might look snazzier than you, with multiple changes of clothes and shoes -- but those are the folks who are throwing their backs out schlepping their giant bags through the town square at 8am, and they aren't going home with two bags full of goodies to share with their friends.
3. Plan too many activities.
I know, I know….You only go on vacation every 5 years, and you *need* to see this, that, and the other thing. As soon as you tell your friends you're going on a trip, everyone who's ever travelled before will have 849287 suggestions of places you HAVE TO GO SEE. A packed schedule is one of the premier ways to quickly destroy an otherwise great vacation. Of course you want to see as much as you can. But imagine if you applied the same approach to your birthday dinner at a nice restaurant -- you'd order the filet, AND the oysters, AND a spinach salad, AND the shrimp cocktail, AND the baked brie, AND the stuffed potatoes, AND the lobster tail, AND the molten chocolate cake, AND the cheesecake, AND AND AND. AND then you would end up puking in the parking lot, broke, and on a lemon water diet for a month. It's hard to whittle down all your desires, but it's much more fulfilling to experience a few things deeply, than whip through multiple places and barely scratch the surface.
4. Try to cover too much distance.
Pick an area you really want to see, and center everything around that. Sure, you can base yourself in Rome and take day trips to Naples or Florence, but that is the equivalent of basing yourself in NYC and doing a day trip to Boston or DC. You *will* encounter traffic, delays, and problems, and creating an itinerary that requires you to drive like a cross-country trucker is a self-defeating exercise. Pick an area, and give yourself the freedom to explore it - to find a great coffee shop or a local artisan, to spend more time at lunch, or to just sit with a drink and people-watch. To feed some swans in a moat. To visit an unexpected sight or museum. To relax! After all, if you wanted to be on a minute-to-minute, demanding, frustrating schedule, you could have just gone to work.
5. Hit all the 'must-see' destinations.
'Must-see' destinations are always going to be chock full of tourists, who are also there because they 'must-see' them. If you feel like you just can't live if you won't get to see the Cliffs of Moher in Ireland, go at dawn, when no one is there. Or look nearby and visit cliffs that are just as high, with none of the tourists (like Loop Head). 'Must-see' the David in Florence? Go in January or February, or be prepared to take in the wonders of the David while listening to multiple tour guides scream about Michelangelo's history in English, German, and Mandarin. Does that mean you can never see popular tourist sights? Of course not. Just know that they are popular for a reason, and therefore, will be highly populated. So think about going in the off-off season; or just pick one or two, and then find small-town alternatives to the bigger 'must-see' sights.
6. "Just wing it" when it comes to meal times.
You don't have to plan every single meal in advance, but if you're in a country like Italy, there can be a wide disparity of food quality in restaurants, especially in the more touristed areas (I'm looking at you, Cinque Terre). Italy is all about the food, and you'll be thanking yourself for doing the research as you sit down to a handmade, memorable, locally-sourced meal rather than a plate of spaghetti and meatballs (this dish is not a typical Italian thing) in a restaurant that has American flags printed on the menu. The UK and Ireland are not exactly known for their food culture, but recently both areas have a big focus on supporting local farms and local food, and lots of farm shops and gastro-pubs reflect that. Search out a few 'destination restaurants', make reservations before you leave home, and get to know the culture you are visiting through its food. If you need to 'wing it', head to local farm shops or markets, or ask locals in a bar where they like to eat.
7. Rack up debt on your trip.
What could possibly be more relaxing than penny-pinching your way through a vacation, imagining how many hours you'll have to spend working once you get home to pay it off? Save up the money you need for a trip *before* you go. I can't stress this point strongly enough -- having spent most of my life in various stages of money panic ranging from sweating through a shirt to full blown bite-your-fingers-till-they-bleed-oh-my-god-I-can't-breathe meltdowns, I am all too familiar with the effects of financial (non)planning. A few years ago I decided to be more like George Costanza and do everything the opposite of the way I had been doing it (travel-wise), and I've never looked back. Get a general idea of what things reasonably cost before you go (e.g. food, lodging, gas), then make a budget. Save the money (yes, this strange thing these days they call 'saved money'), and stick to your budget. You don't have to count every dollar (or Euro or Pound) when you're on vacation, just be aware that you are in the ballpark. When you get home, if you've gone a bit over, it will be by a few dollars. And you won't be saddled with thousands of dollars in debt you have to pay off for that 'restful' vacation.
8. View your entire vacation through a phone camera.
For the love of all things holy, put your phone down. Unless you are a travel writer or a health inspector, you don't need to document every bite you put in your mouth. No one is going to look at those pictures anyway, including you! While you're taking 351 photos of that double rainbow, it's dissipating, and guess what? You missed it. Human eyes are much better at capturing scenery and natural beauty than your iPhone, even if it is a 6. You're going to see so many things you want to record for memory's sake, but wean yourself away from having the phone be your only 'recorder'. What sounds are happening? Are there interesting scents? What does the sun and breeze feel like on your skin? Try to put those 'markers' in your brain, and when you get home you will be able to recall these precious moments more accurately and with more pleasure. If you count on the phone to do all the recording for you, you'll miss a lot of the details, and you'll also be really disappointed when you accidentally drop it in a full toilet at the airport and you have to 'mercy flush' it.
9. Make a checklist and base your happiness on it.
Don't make a checklist of the things you 'need' to see, 'need' to buy, or 'need' to do while you are on vacation. If you have some really strong feelings about goals you want to achieve, pick one or two, make sure they are doable (e.g. the sight is open to the public), and get it done. A checklist can be a harsh mistress and a helluva way to spend each precious day you have off. Try to make your goal learning something new, experiencing a new place, finding something you've never seen before. Allow yourself to have the time and space to satisfy your curiosity ("What's down that small street?", or "I wonder what 'cervello' is?" -- spoiler alert, it's brains). Make your goal to end each day having experienced something new, and feeling rested and invigorated. You'll thank yourself when you get home, and years later when you recall the vacation with fondness.