I almost always tuck into skirts, because it creates a better proportion on my long torso and long rise and lets me show off my smaller waist even if the top doesn't have any built in waist definition. However, for a skirt tuck to work on me, the skirt has to hit at my natural waist and fit snugly there to keep the top in (although sometimes I just paper bag an overly large skirt with a belt!). The only time I don't tuck into a skirt is if I'm wearing a short, waist defining top.
With trousers, I used to never tuck, because nothing ever hit my natural waist, and tucking lower down just obscures my curves. Now with forum encourage I'll tuck occasionally into (on me) my mid rise skinnies, especially if I'm wearing a jacket over top. But the vast majority of the time I don't tuck into my skinnies. This winter, I frequently wore a couple pairs of vintage wool trousers, that hit my natural waist and were cut in a more generous manner, and I discovered how comfortable and easy it was to tuck tops in those! So now I'm hoping to find a couple pairs of wider leg, very high rise (it takes 12-14" to hit the smallest point of my waist) trousers for warmer weather to replicate the look. I've already found one pair and wore it yesterday actually!