Beware! Lengthy screed about lessons and accents (it's a quiet day at the skunk works).
I guess I was lucky in the voice and guitar teachers I had early on. My first voice teacher was Edna Bianchi, a retired operatic soprano and my second, George Hotchkiss Street, had been a singer (bass-baritone, more like my own voice) and choir director. Neither of them tried to push me into a particular repertoire or style. They both had me doing a lot of vocalizing with scales, arpeggios, and other exercises, teaching me breath-control and getting me to relax my throat and let my voice come out. They both asked me what sort of songs I wanted to sing, and that's what we worked with. Their focus was not on how I should sing the songs as far as style was concerned (they both said that I probably knew that better than they did), they focused on voice production, such as breathing, relaxed throat, and projection. Both were sticklers for clear diction and phrasing. Vocal technique, not style. They managed to turn my "frog in a rain barrel" into a halfway decent sounding singing voice. Not particularly operatic, but at least fairly listenable (well, anyway, not too many people get up and make for the door when I start to sing).
Mr. Street had me bring my guitar to the lessons and accompany myself while I was singing. He would often stop me in mid-song and ask, "Okay, now what, exactly, does that last line mean? The one that starts—" and then he'd quote the first word or two of the line. What he was pointing out to me was that I hadn't really paid attention to what the line meant. I had just been singing it by rote, without really understanding what the heck I was really singing about. Very valuable lesson!
My first genuine guitar lessons were from Walt Robertson (two Folkways records, and he had a local television show at the time). Chords, strumming and picking patterns, and lots of songs. After about six months, he said he had taught me about all the guitar he could, and suggested a classic guitar teacher. Over several years I took classic guitar lessons from three different teachers, and took four months of flamenco lessons from one of the guitarists who was playing at the Spanish Village during the 1962 Seattle World's Fair. I picked up folk techniques by watching, listening, and trying things out. Still at it. And with the classic, I'm no Segovia, but if I've taken my vitamins and have a good tail-wind, I can manage to play a few fairly impressive concert pieces.
How do I apply that to folk song accompaniment? I don't, all that much. I generally keep my accompaniments pretty simple and straightforward. But on a few songs, where I think it might be appropriate, I pull out the stops and try to handle the guitar as if it were a lute (Greensleeves, The Three Ravens, a few others).
None of the music teachers I took private lessons from tried to push me into doing things I didn't want to do or force styles on me that I didn't think were appropriate for the kind of songs I chose to do.
If a teacher insists on pushing you in a direction you don't want to go, find another teacher.
Accents and dialects: There have been a number of threads and a lot of comments about using accents and dialects that aren't part of your own ethnic background. Lots of people seem to feel that it's "phony." But unless you are going to limit the songs you do to one category (placing an arbitrary limit on yourself, which I, personally, am not about to do), one can hardly avoid it. I do a fair number of Scottish songs and ballads (even though I was born in Los Angeles and have never been to Scotland, I feel that with a name like Firth, and considering that my great-grandfather came from Scotland, I can claim some rights in the matter), and, if I do say so myself, I am pretty good at imitating accents and dialects of various kinds.
I challenge anyone to sing songs like McPherson's Lament or Bonnie Dundee without adopting a Scottish accent. And I'd say that singing something like The Braes of Killiecrankie would be impossible to do in American English. And how, exactly, is one to sing "Oh, me name is Dick Darby, I'm a cobbler. . . ." without a touch of the Irish?
Some people can't do accents and dialects for sour apples, and if you can't, you probably shouldn't. But if you can, then have at it, say I!