We all know the generic problems with advice: we're not ready to listen to it even if it's good; it's bad; it comes in a package that guarantees we won't follow it; it's more about power than wisdom; we have to, apparently, make our mistakes; we just don't like the person giving the advice; and so on.
As to problems with advice given to younger or new writers (new to poetry, let's say, not writing in general), . . . .
1. Most of it is too broad. I think I remember being a young poet (I believe it was in the late 19th century), and I recall hearing and/or reading "write what you know" and "show, don't tell." The latter remains pretty good advice when accompanied immediately by examples; nonetheless, fiction especially depends on telling, often to speed things up. And the triumph of imagery has been so widespread that one gets bore with it sometimes and years to hear a statement or an opinion. "Tell me something, bro! Speak it, sister." As to the former, "write what you know," it's hard to know what one knows. If we take into consideration the mental landscape, we know lots of things we haven't experienced directly. Some young writers have been known to read a lot, so that's part of what they know, even if they work on a farm or program computers. Plus, we imaginative writers are supposed to make stuff up, yes? And then--maybe this happened/happens to you--you hear these or other general bits of advice, and you don't disagree, but you think, hey, that's great, but what about this piece of writing I'm working on? I first read The Triggering Town (Richard Hugo) many, many moons ago, but I remember that the advice in there that stuck with me the longest and proved most useful was the very specific stuff: arbitrarily repeat a sound from the previous line of poetry in the next one; get rid of connectives (often, not always) like "but," "although," "however"; don't throw bad poems away because you can always strip them for parts; don't erase a word--line through it so you can still see it. One of the best pieces of advice I received from Karl Shapiro concerned writing/practicing blank verse (I paraphrase): "Just memorize a line from Shakespeare, keep the rhythm of that specific line in your head, and write." I think I first used "But, soft! What light through yonder window breaks?" because I still had visions of Olivia Hussey in my head and because (nerd-alert) I kind of liked that big caesura early in the line.
2. The advice isn't tailored enough to the individual writer. Classes in creative writing have their legions of critics, and Lord knows lots of the classes probably have it coming. One advantage (for me the teacher and them the writers) of a semester-long class, however, is that I get to see how Ivana's (to invent a student) poetry takes shape in her particular case. I have some sense of what she's going for in a new poem--in terms of phrasing, tone, attitude. I have a sense of the strengths and weaknesses that show up in Ivana's first drafts, often, and I know that some of these alleged "weaknesses" are just point on the path as she moves toward the final draft, so I'm less likely to over-react to them, or to preach about them: "show don't tell!" And I get an opportunity, often late in the term, to suggest, "Why don't you try a different kind of poem?" So Ivana may have written three fine poems of a certain kind in a row, and that's good, but I can say, in effect, I don't think the class ever looked in this room as Ivana and I and the class take the tour of the poetry-house. And usually Ivana will say, "Oh, yeah! --Yeah, I'd like to try that kind of poem." And that spark--the zest with which a new or experienced poet goes after something new--is often more valuable than an effect provided by more generic words of "wisdom."
3. It's not so much at all young/new writers have to make the same "mistakes" other writers have, and it's not so much that general advice is necessarily bad; it's that a lot of things a young/new writer has to work out, through much writing, is sui generis. The young/new writer has to work out this particular problem s/he has when writing about the one river she knows well. And s/he probably has to do it the way a lot of left-handed batters in baseball have to work on not getting struck out on the inside-and-low pitch: lots of batting practice; many scribblings. It's not wrong or unhelpful for the coach to say some advice during batting practice, but without the batting practice, the advice is a pitch in the dirt, too.
At any rate, my advice to younger/new writers is, um, well--I don't think I have any at the moment, and the advice I've published is, having been published, easy enough to avoid or ignore. You go!