1: Do pee pre-emptively
Public toilets are unnervingly scarce and even when you don't need to go, you might just be surprised at your output. Plus, worrying you won't find a toilet somehow shrinks your bladder. You often have to pay to pee, so carry a stash of 50c coins for the angry-looking troglodytes staffing the underground toilets.
2: Don't try to co-ordinate your footwear with your outfit
Ballet flats are out. So are comfortable sandals. Only big, ugly walking shoes can save you from blisters that won't heal until you're home, even though you've worn sensible shoes every day but the first.
3: Don't try to cover too much ground
Be nice to your feet and take the metro, even when it only looks like a short walk. And consider bike tours, especially in flat, compact cities. Your feet will still ache by the end of the day, but it won't be as bad.
4: Don't scrimp on calories
You'll walk off all that pain au chocolat in Paris, stroopwafel in Amsterdam and currywurst in Berlin. Plus, it's the real deal, so you have to try it.
5: Don't assume free means free
Most of the "free" walking tours have booking fees, expect tips, or both. Plus, most of them are led by over-excitable Americans who dress like The Wiggles and shout at you.
6: Don't book everything
Sure, it's a good idea to book hotels, flights and trains, but when it comes to activities, you may change your mind, depending on what you feel like doing and what you have time for.
7: Don't overstuff your itinerary
Otherwise, you'll be rushing rather than savouring things. Instead, have a few options on your list and decide on the day.
8: Don't try to tick off all the tourist hot-spots
Sometimes strolling through a Parisian street market or people-watching at a park is more fun - not to mention free - than queuing to see the Eiffel Tower or the Tower of London. And sometimes it's the unexpected detours that make your day.
9: Don't try out your schoolgirl French or German
Well, not unless you can understand what they say back, talking far more rapidly than your teacher used to. Parlez anglais, s'il vous plait?
10: Do beware scams
Giving a new meaning to the term finder's fee, con-artists across Europe "find" a gold ring as you're passing and try to sell it to you at a bargain price. Who'd have thought they were brass not gold?
11: Do double-check that breakfast is included
Otherwise that hotel buffet of rubbery eggs and cold toast will swallow the whole day's food budget. And when breakfast is included, who'll notice that banana going into your bag rather than your mouth?
12: Do avoid the stupid-tourist charge
At restaurants, check the bill and query it straight away if necessary. Avoid the expensive, "touristy" restaurants and stalk the locals to see where they eat. Better yet, browse street-food stalls, or go to the market and you've got yourself a picnic.
13: Don't over-tip
Ten per cent of the bill is enough. Don't keep giving them more until they smile. They won't.
14: Don't sit down
Well, not unless you've paid for your seat: some establishments charge less for take-away coffee and pastries than they do if you're eating (or drinking) in. Flout these unsaid rules and you get the evils.
15: Do take snacks on trains and flights
Otherwise you'll get hangry and end up paying $20 for a stale, wilted filled roll. Oh, and when they say it's vegetarian, they mean it has vegetables. And chicken.
16: Don't treat your guidebook as gospel
Either that great falafel place has moved, or 30 people in khaki pants are already queueing, leafing through that same guidebook.
17: Do take only carry-on luggage
If you're leaving town later that day, you can wheel your carry-on in the meantime and avoid having to return to your hotel. And it's not much fun lugging a heavy suitcase up and down the stairs at all the underground metros. Plus, checked baggage on European trains often arrives at a different time or day to you.
18: Don't photograph everything
No one - not even you - wants to see those 300-plus photographs of architectural sculptures on every old building you passed. What do they say about experiencing rather than recording?
19: Do take a lunchtime siesta in summer
And some deodorant. Forty-degree heat ain't pretty, just whiffy, so when in Rome, do as they do and make yourself unconscious.
20: Don't dwell on your mistakes
They make good stories to tell friends and family later.
Disclaimer: Sarah Lang enjoyed her holiday.