I have an Android and use Timestamp Camera Free. I don't know if there is one for an iPhone or not. It's very easy to use and very intuitive. Hopefully some of the Apple fans will come on and let you know about iPhone. Or if there's a better option.
Just Googled and it appears there is a version for the iPhone.
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apps.apple.com]
I usually take my pictures in landscape (phone on it's side) orientation. But it all depends on what you are trying to capture.
Also, on occasion, moving 10-20 feet will give you different addresses. I took a picture last week on a shop in the parking lot and it gave me the address of the store 259 feet from where I was standing (I Google mapped the two addresses). I believe it depends on how cloudy it is and if there are tall buildings obstructing the GPS signals.
Good luck on your first shop. Come back and let us know how it went. And remember, not all shops go perfectly. But if they don't, just learn from them. The more of each particular shop you do, the better you will do them. Practice makes perfect.