3Ts,
Is this work or vacation? How old are you? Travel planing is more important than how to pay. Each place will have it's own feel and flavor. Most places I go to, Asia, Europe and Mexico/South America, have plenty of ATM's and accept credit cards. But I only use credit cards at very trusted places. Who knows what happens to your card as they walk away to process it.
I always get about $100 worth of the local currency or more if I'll using taxis a lot. Know the exchange rate and go to the ATM at the airport where you land. Some ATM's are tied with a currency exchange place, avoid due to bad rates. If the ATM asks, "do you want this deducted in USD or the local currency?", always go for local currency because the conversion rate is always lower than your own bank. Even some hotels will have local vs. USD.
Get one of those money clip wallets and carry it in your front pocket with your phone, one pocket! That way in sketchy situations, metro or crowded places, you can keep one hand in your pocket and one hand free. If you see a disturbance on a street, keep walking. Often these are staged to have a bunch of spectators with pockets ready to be picked. Carry only one credit card and small amounts of cash at any one time. I leave the rest of my credit cards/ATM back at the room. Have a copy of your passport in the money clip to meet any local requirements of "ID". A real bummer to loose your passport!
Back to being well planed. Don't try to "figure it out as you go". Google is your friend and just about every question you could think to ask is covered on discussion boards. My wife and I travel in small towns in China after I complete my biz trip. Most would say we are crazy. But if you can write down all the steps it will take to get from point A to B and research it, it is not bad at all. As mentioned, know the exchange rate. When a taxi guy tells you 600 Czech crowns, you need to think , "how much is that?" Have all your hotel details printed out, with a map of the city and it marked. By now you should know from your friend Google, it's about $12 for a taxi to your hotel. If the taxi guy comes back and says $40, walk away. I will not give them a second chance, you they tried to cheat you once! Oh, and always have as close to the exact change as possible.
Take advantage of the front desk. If you are planning to head out and see some sights, get two notes written in the local language; !) please take me to "fill in the blank", 2) take me to the hotel "fill in the blank"
Ask locals for help, most are friendly. Generally I target younger guys that are in business attire. They most likely speak English
If you are spending your $$, take metros or what ever train goes into town.
Flying from city to city. Be aware when your flight departs and lands. Some cheap flight get in late. I prefer mid morning flights getting in during the day light.