Hello! I have no success in propagating succulents from leaves as of yet. I cut off a leaf, let it calus for one or two days, place it horizontally on soil with much perlite, and spray when the soil is dry. But they all eventually turn black and swishy, which I suppose means overwatering? Am I supposed to leave the soil totally dry? Since it is so shallow it dries in no time. I would appreciate if you shared your success in that, how do you do it?

You need the whole leaf for most succulents. It has to be intact all the way to the base, which means you can't cut it off, you have to (carefully) pull it off, or cut it from the stem by carving into the stem (in extreme cases). Usually it's best to use a sideways motion to pop off intact leaves from rosette succulents, rather than pulling away from the stem. Some of them can be reluctant to let go of their leaves so take your time and wiggle the leaves for best results.

The rest of what you're doing sounds right. I like to lay the leaves on the same mix I would use for the mature plants (50% pumice), and use a container that is wider than deep. If you're just experimenting, you can lay the leaves on top of the soil where there's already a plant. Just water when the soil is dry, when you would water normally. No misting or special treatment required, unless you like to do that. It is important to keep leaf propagations out of direct overhead sun until they are pretty far along.

The way you know it works is when the leaf sprouts a tiny new rosette at the base, along with baby roots. The leaf will shrink up to supply water to the baby plant until those roots are functioning. Sometimes 2 or 3 heads sprout. You have to be patient after that point and try not to disturb the very young rosettes until they are maybe the size of the original leaf, and properly rooted.

Some succulents cannot be propagated from leaves. What are you trying to grow?

Oh, now I get why it didn't work @Baja_Costero, I didn't really pull them, some of them even were ones that had fallen from the plant! I see, I need to have a "deep" edge there where it will root. Thank you!
I am trying to propagate some types of Crassula, the ovata and some that are similar to the Jade plant, but with bigger leaves. And I am also trying this with a Clusia (Autograph plant). I will try this with the sideways pull you mentioned! Do you mind if I show you tomorrow, like I could photo the ones I pull, and see if it's OK? Just not to go through all the mushy thing again?

Yes, of course. The jade type plants should be possible from leaves. They can root after falling on their own without any effort on your part. I have no experience with Clusia.

Baja_Costero said:Yes, of course. The jade type plants should be possible from leaves. They can root after falling on their own without any effort on your part. I have no experience with Clusia.

I have never heard of growing Clusia from a leaf but they do grow very easily from cuttings. Just cut off a piece of stem and stick it in the ground.

Thank you @Daisyl, good to know!