How do you tip gracefully? I always feel terribly embarrassed tipping hotel drivers or doormen. I have no idea why, just do.
The only fixed rule I have so far is never to put a tip on my debit card. I always make sure I leave cash, so the wait staff get the tip immediately, instead of having to wait. Other than that - I'm lost.
Some places are more tip happy than others. NYC and Vegas are probably the two most tip happy places on earth. You get used to the ritual after a while. When I was young and poor, I tried to avoid tipping as much as possible. As I have gotten older and a bit more prosperous, I have come to tip more generously than in the past. I feel if you want a relatively trouble-free consumer life it makes sense to overpay for services and underpay for goods. I will eke out every penny of possible savings if I am buying, say, an iPad. But if I'm renting a hotel room I might go ahead and book it directly from the hotel and tip the maid $20 when I leave. This is especially true if it is a hotel I plan to go back to on a regular basis. It ensures I always get the best room and attention they have to offer.
Your idea about not putting tips on credit cards is a good one. I tend to follow that as well. But you will want a record of the transaction if the tip is part of a tax deductible expense, so that needs to be factored into your thinking. One bit of advice I have is to stock up on singles and fives before you leave so that when you are out there you never get stuck without the necessary denomination for a tip. Also, when in foreign countries, always tip in US dollars. Without exception. Dollars are more valued in every country of the world than the home currency, and tips using dollars are very much appreciated. This is particularly true in third world countries.
I usually tip $2 for basic services such as a parking valet or the guy who puts my clubs on the cart at the golf course. That's the baseline. If I have a special request (say I ask the guy to park my car in a covered spot instead of one open to the weather), and the person does what I ask, then the tip goes to $5. It can go up from there, depending on the situation.
My father once once tipped a guy in Vegas $100 to put us in the front row of a George Carlin concert. That was in the late 70's when $100 was a goodly amount of cash. He loved Las Vegas and the whole tipping culture there, where basically money speaks very loudly. Me, not so much. I pick my moments.