I’m using classical grip–both hands.
How do you’all do slides?
A combination of lipping down or up, and taking your finger and either moving your finger across (perpendicularly) or along the flute (up or down the length, toward the head or toward the foot).
Kevin Krell
carefully
I suggest, at your age 
…and wear a helmet!
Finger speed mostly, there is some proximity things going on.
Took a bit of slow practice. Very slow.
The open holes make it easier.
Thanks.
John Skelton, at a whistle workshop, advised us to avoid
the ‘siren effect’ when doing slides. Playing whistle
one just grazes the side of the hole close to one’s
hand as one straightens the finger. It’s a more subtle
slide, it’s quite lovely, in fact.
I can slide alright on the flute, but I’m trying to duplicate
on the flute
the ‘subtle’ slide on the whistle. I still sound like
a siren.
The classical grip doesn’t help here.
I’m trying to slide from the bottom edge of the hole,
that is, the edge near the bottom of the flute,
not from the whole hole.
Slow practice is good, definitely.
Thanks again.
…having finished my coffee and had a go at it on the open holed flute…
I see that I was wrong!
For the left hand I, usually, pull the fingers off of the holes, the right straightens.
Wish I could hear a clip demonstrating the undesireable “siren effect” and the more subtle slide.
The more listening I do to the old timers, the less I’m using slides. At least, not in the way I used to. Correct me here please if I’m misunderstanding: the Martin Hayes style (I know, fiddle not flute, but the strongest example I can come up with) plays lots of slides. But the traditional style, much much less. Slides bring a more modern, jazzy sound.
Whistle music-- more slides.
Flute-- much less.
Yes? No? Anyhow, I figure I’m better off stylistically just going for simpler melody with a few cuts, taps, and rolls while I’m developing as a player.
Maybe the wrong thread for this question, as Jim wants to know more about technique. 
Thanks.
Jennie
I don’t expect that either Jim or I were thinkin’ Irish trad. so much…
…although I’d think ya could work 'em into an air or two. 
I think you’re right but I don’t listen much to old recordings (my loss).
I’ve noticed that ITM players tend to avoid sliding downwards. Kevin Burke speaks briefly of this in his instructional video and says that sliding down has a “sinking” quality, hence one would not use it to excess. I find it is an effective ornament for fiddling (e.g. B–>Bb–>B) but never execute it on flute or whistle. Maybe I’ll give it whirl…
Slow slides can sound a bit cheesy/old tyme but I think it can be great on fiddle (e.g. Martin Hayes, Eileen Ivers).
For the siren effect,
just play an E, say, with your finger squarely
covering the hole. Then, from that position,
slide it off the hole. You get a shift in pitch starting
from E and ending at F#–sort of OOOAAAh.
That’s the siren.
For the subtle effect, sliding up to F#, place your
finger over the E hole on the whistle so that it isn’t squarely on it,
but is creasing the inside lip of the hole.
My finger is straightish, pointing a bit upwards,
so that most of the hole is uncovered.
Slide your finger away from you, over
the inside lip and then off the hole entirely.
This gives you a more subtle sounding slide.
I haven’t thought much about whether slides suit the flute.
Must think about it.
Just to make sure I understand you correctly. For a siren-like slide you start with a fully covered hole and end with a fully open one. Whereas for a subtle slide you start with a partially covered hole, but still end with it fully open. Have I got it?
Yes, precisely. Try on a whistle.
So you just crease the edge of the hole in doing
the slide and end with the hole open.
Sounds very nice.
Less sure how to do this on a flute.
I think proper and clean execution of a slide is fairly dependent on the soles of your shoes and the type of floor.
I have seen the best minds of my generation
destroyed by hyperventilation.