This is an idea aimed at the needs of general succulent aficionados, with the goal of ensuring a strong start for newly acquired succulents.
If that appeals to you, proceed...
Succulents for sale are generally (and should be) fully rooted in their container, or nearly so, if they are grown right. The goal of the succulent grower should be to arrive at the largest size plant per unit pot and soil, so as to maximize return per unit cost. There is some prestige in this, as the larger product looks most resplendent. But mainly it's a matter of economics.
Check if your succulent is well rooted in its container. There are various ways to do this. An extra-large plant for the size of its container will normally be well rooted. Otherwise, first look at the drain holes, to see if you can identify roots near the holes or exiting through them. Sometimes new heads will be sprouting from them. Second, "pop" the soil upward with light pressure on the lower surface of the container. If you can feel the whole root ball moving upward as a unit, there's a good chance roots are keeping it together. But if pressure on that surface simply results in the displacement of soil, the plant has likely not rooted properly down there. You may want to skip the repot if this is the case, and allow the plant to proceed in its current container until it's filled. When in doubt, wait for the plant to fill its container. Succulents are not needy about space.
The truth is revealed when you unpot your new succulent, of course. Be extra careful to keep the root ball intact if possible. Pay close attention to the roots, to judge their general health and to exclude the presence of insects or other pests. Pay close attention to the soil used in the original pot, and see if it is different from the one you have chosen. If that soil is questionable for some reason (it worked so far, but that's no guarantee it will work for years more) or if it is radically different from the one you want to use, then do your best to get it out of the root ball, without breaking any more roots than reasonably possible.
A well rooted plant will pop out intact and the root ball will retain its original shape. If this is the case, just drop the root ball on top of the appropriate amount of soil in its new pot, and fill in around the edges. However, if the plant comes out partially rooted, or you decided to bare-root it, you will have to exercise patience and deliberate intent when you separate the roots from the soil, in order to avoid breaking roots or damaging them. Pot the plant up carefully afterwards, spreading the roots so they are positioned to explore the whole pot, and fill in around the edges so that the soil level remains the same on the main stem as it was before. The pot should be roughly proportional to the roots, plus a little extra growing room. Overly large pots (relative to the size of the roots) are generally to be avoided, as they will tend to stay wet at the bottom (without disciplined watering) but not in the zone where the roots are, near the surface.
Most importantly, do not water your newly repotted succulent for a few days to a week, depending on how much you had to handle the roots. The goal here is to avoid submerging broken parts in dirty soil until they have had some time to heal. Then water deeply, until water comes out the bottom, and wait for the soil to dry out before watering again.
There are exceptions to every rule, but most succulents prefer a pot that is wider than deep, with holes at the bottom. They tend to do better when given gradual stepwise increases in container size, rather than big jumps, at least without really careful attention to water. In climates with high humidity and rainfall, a fast-draining soil is imperative (50% organic, 50% perlite/pumice/equivalent gritty rock). Unglazed clay pots may also work better in those climates, as they can lose water through the sides of the pot as well as the top, making them dry out faster.
Use soil with fast drainage, for example regular potting soil mixed with an equal volume of perlite/pumice/gritty equivalent (avoid fine sand and vermiculite). Prepackaged cactus & succulent mixes often are a bit too organic and still benefit from the addition of some rock.
It may be helpful to time the repotting for when you expect the soil to be going dry at depth (a bit before you would normally water). You can then use the exercise as an opportunity to look at the soil moisture directly and see if you were guessing correctly. If not, maybe consider changing how often you water.
Avoid repotting succulents during late fall and winter if they will be experiencing dark and/or cold conditions. Repotting is generally best done in the spring, when in doubt, because of the strong light and warmer days.
