Hi Nero,
I've done quite a bit of OS over many years, as Hikari said unless it's buisness or conference go with someone. Even a relative if need be

Can tell stories about that as well

Security. Use the Hotel safe to store your passport and plane tickets. Photocopy your passport and tickets. If you can keep a copy with you and a copy at home with a friend. Take two credit cards. Don't flash a lot of money, I still use a money belt under my blouse/sweater and have enough in my purse for items. I keep extra cash in the hotel safe if need be. Be aware of pickpockets, the ones in Italy are really good, watch out for the baby trick. I had a friend in Paris who got on the metro four guys crammed around her, one took out a knife, sliced her bag open and took her wallet. She couldn't move as she was crammed in, they just got off at the next station a few seconds after

. Don't carry, take, use, think, about drugs. Never let your credit card out of your sight. I used one in Malaysia at the hotel I was in. Only used it once at the reception desk, it was scammed three times.

Sorry if this sounds like Oh No

Never let on you're from the USA, as Hikari said; lots of Europeans don't really like the USA after your ex-president, your new one is popular though. I happen to love you B&G's.
Never get drunk, unless in your room. If in a tourist spot a really cute guy or girl chats you up, it is probably not true love

Be very sensitive to local issues. I remember in SF being asked by a too belligerent hotel guest, out of the blue BTW, which is more beautiful the SF Bay harbor or Sydney Harbor. The answer is obvious, Sydney, I of course said San Fran, he was happy with that.
Of course make sure you have medical insurance etc. Don't break your wrist in Delhi, I had to fly back and have it re-broken and reset, then fly back again, not a good trip

Take lots of pictures. Go to local markets. Never buy stuff from souvenir shops, use banks for money exchange, or use your credit cards only.
Smile all the time.
Paris is great. I like the French, try to speak French, no one likes English speaking people expecting everyone to speak english, even if the do. If at first someone doesn't understand, shouting doesn't help

Had that done to me in the reverse it was hilarious and very offensive at the same time. Paris is expensive. Full Stop. Expect to queue for hours for the 'famous' sites, particularly in peak tourist holiday time (6 hours for the Eiffel Tower), I waited 5 hours to get into the Lourve, complained to someone they had waited for nine, some one else had bought prepaid passes and got in without queuing Mmmm. The Mona Lisa is a very small painting of a not very attractive person, few, I think, realise how small it is. I do know BTW that size isn't everything

Plan to see some of the 'lesser' sites, many are gorgeous. If a 'tourist' bus trip of the city is available think about taking it, they are often quite cheap and show you things you will not see. Locals think they are crap but as a tourist don't try and think like a local. E.G most Londoners have never been to the Tower.
People are usually very willing to help people. Listen to the hotel staff and ask them questions. I remember in LA years ago I was going out for a walk about 9pm. The desk staff stopped me and asked where I was going and they would get a cab for me. I said I was just going out for a walk around. They just said no; you won't come back from a walk around here. Scared the c**p out of me. They were not joking

And most of all - ENJOY IT.
Even with all that and no doubt many others will join in. I love OS travel and also local travel. I have to admit I have had a few scrapes but never a major problem.
The rattling wrist bone and the OT full of s**t was a high-light

Someone picking me and my friend up in an ox cart and taking us to their home and insisting we stay, organizing their family and friends to come to a party and meet us was a highlight. I'm pretty sure I had more cash in my purse than the village had in total, and I didn't have much, but they were so pleased to meet people.
I won't mention the egg breakfast in Vietnam

But it was supposed to be a treat

I'm not sure, but I always try and treat people with respect. I hope that in doing so they will treat me that way as well. Mainly I think most people aspire to the same feeling.
Being invited to a, home made, brandy drinking party in (then) Yugoslavia. I still remember that hang over. But it was great. For the month I was in the town after, EVERYONE, new me. I was greeted everywhere and warmly and friendly. Even the 'secret' police were friendly.
Sorry Nero. You have tripped my wires. Time to travel again.
Hugs Bro
Cindy