Actually, most/all countries print money. Ours does for sure. To be the only major country that didn't do this would be very problomatic.
1) Comparative interest rates between governments is probably the biggest direct factor of the value of one currency to another. But it's more of a balance, rather than A causes B.
Look at it more like supply and demand. There is a big demand for US currency. If we paid a higher interest rates on our bonds, that would increase demand for those bond, thus increasing demand/price of our currency.
We don't offer good interest rates on our bonds, because we don't have to. There is a high demand for them anyways, especially in times of crisis like now.
2) Some countries actually want the value of their currency to be worth less. China has seen massive year over year gdp growth for the last 20 years or so, and was criticized for the whole time by our government for artificially pegging the value of their currency too low.