Hey, where did you live? I lived in Grand Forks for years. I’m a UND graduate. My wife is from Devil’s Lake. I live in the Cities now but I know ND well.
I think part of the key to the accent is getting the cadence right. There’s a lilting quality, a sort of rising at the end of sentences. Sometimes it sounds like every sentence is a question. “I’m going to the store” can sound like “I’m going to the store?” You have to be subtle, though, don’t over do it. It’s just a hint of a question.
I grew up in the 'burbs of Minneapolis and said “uff da” all the time. Probably more due to the fact that my paternal grandparents were first generation from Sweden. My neighbors would say the “Ohfers” as in “ohfer cute, I like your hotdish doily”.
As a1997xf11 pointed the long “o” sound out, the “t” or the “th” dipthong is sometimes substituted with a “d”. Although, sometimes the “th” is substituted for a “t” consonant as in “Da best way to go up Nort’ is to take Hiway 169, ya know?”
Diogenes the Cynic pointed out that there is the bit of a question tone at the end of sentences. For instance, ordering in a restaurant: “I would like the steak and some green beans?” It seems to me that this is used so as not to offend someone by being so brash as to have an opinion on what you want. (This gets into the whole area of ‘Minnesota Nice’ which could get ugly)
The Minnesotan accent is not as often encountered or heavily pronounced in the “cities” (Minneapolis/St Paul metro area) as it is out-state. Going up nort’ towards Bemidji, Brainerd, Ely et al and you’ll encounter the “Minnesota” accent which is really more of a scandinavian accent.
Forget that last post, I don’t know where that came from. I’m in Grand Forks. Been here 10 long years after growing up in Milwaukee. Just imagine MY dialect. 
And that’s the way it should be, damnit.
I agree, as a matter of fact there used to be a store not far from our house growing up called Pic-A-Pop where one could choose from an assortment of pops in 24 packs (IIRC) and then return the bottles and get more. I miss that, their black cherry pop rocked.
I beg to differ. POP is my father, or coincidentally, what he used to do upside the back of my head when I was a smartass. SODA is carbonated water, which can be sugared, flavored, or both.
Diogenes, I just moved over from Minot this past July. Spent three and a half years up there.
Tripler
And I made it a point to avoid all the HostFests I could.