What factors will shift the supply and demand for currency?

Confidence in the economy. If the economy of the country is doing good, it is likely that the confidence in that currency is high, raising the demand. However, when the economy is sloppy, the lack of confidence brings down the demand level.

Level of exports and imports

Relative income changes (Higher income in other countries => go on holidays and thus rising demand for other currencies.)

Relative interest rate (High interest rate => high return => people invest more in it)