Generally, the best way to get local currency is to use local ATMs when you arrive. Your bank will usually charge you a small fee to do this (typically around $5), and you may also get charged a fee by the local bank, but you will generally get a reasonable exchange rate (as opposed to local banks or money exchange desks).
Since you’re getting charged fees we recommend taking out a few days worth of local currency at a time, and an amount that you would feel comfortable carrying around (e.g. $100-$200). No point in carrying $500 on you just to avoid $5 of ATM fees!
At most places you can pay with your creditcard too. Ask your local bank about possible fees when using your card abroad.