Here are a few tips that might prove useful when in Jordan:

They usually buy USD at 0.7085JOD (0.7080JOD in summer-time) and sell USD at 0.7090JOD (0.7085JOD in summer-time). That is how they make money (they do not charge a separate exchange commission). Much better than exchanging at a bank because currency exchange shops do not charge an extra exchange commission as banks do.

NOTE: the worst rate you'll get is at Queen Alia airport. But still, the commission they charge is nothing compared to what you would be charged in Europe or USA. It wouldn't hurt to exchange like $100 or $200 at the airport so you have Jordanian Dinars on you. I suppose you must, because you'll need 40JOD to pay for the visa at the airport (check visa cost - it changes regularly!) and maybe 20-25JOD for the airport taxi.  

Within Amman, you can hail any yellow cab. Make sure the driver resets the meter. Average ride would cost around 3-5JOD. Alternatively, you can use UBER or KARIM. You can check availability and compare prices via google maps. 

NOTE: you will need to have your passport with you to purchase a sim card.