How much sun succulents need
Since you're growing your succulent indoors, pay attention to the color of the succulents you're purchasing and tend toward the green ones. Brighter succulents with colors like orange and purple might look pretty, but they'll likely require more sunlight than you can provide, so stick to the darker, heartier ones.
Green or not, supply them with as much light as possible. Outside they want something like six hours a day, but inside don't even think about it in terms of hours. Just get them in the sun and keep them there. Place them near the window that has the most light per day in the brightest area you can manage, as close to the window as possible.
You'll be able to tell if your plant isn't getting enough sunlight if its leaves start to stretch. Your succulent child is bending and expanding in a feeble attempt to get as much light as it can, so the least you can do is move it closer to the window or to a brighter area. If that's not possible, you can look into purchasing a grow light, which mimics sunlight and could save your little plant's life.
The best soil for succulents
In soil as in pots, you're going to look for something that promotes drainage. The easiest way to find proper succulent soil is to look for a cactus soil mix that's categorized as "fast draining." If you're more of a hands-on plant parent, find soil with quarter-inch particles that contains perlite or mix perlite into soil yourself. Perlite is volcanic glass that’s heated until it pops and expands, which makes it lightweight and creates a bunch of little air compartments. The air pockets mean perlite is porous, so the water drains easily, which, again, will keep your beloved plant from rotting.
So remember: Supply your plant with as much light as possible, make sure its soil has proper drainage, and soak the heck out of it once it's completely dry and only when it's completely dry.