Leaves can be placed indoors or outdoors. Below are some tips to make sure they last.

Transit and storage

Protect the edges and tips of the leaves in transit and storage, using bubble wrap, air pouches, of best of all, space! Keep the leaf away from anything it might bump into, or rub against during transit

Metal loop

Leaves have a loop embedded in the back so the leaf can be hung on a wall/fence/tree. For smaller leaves, this loop is made using garden wire which can be manipulated by hand. For larger leaves however, a stronger gauge galvanized metal is used.  If you need to make changed to this loop, use two pliers/wrenches. One can be used to hold and support the metal close to the base of the leaf, while the other can be used to bend the metal loop into another shape.  If you try to bend this loop without supporting the wire where it exits the leaf, you risk putting a lot of strain on the concrete and may break the leaf.

Winter

I recommend all outdoor leaves are taken inside during the winter.  This is especially important if the leaf is placed in a horizontal position where it may collect snow or ice.
(Anecdotally, I do have leaves that are hung on a tree or fence above the snow line which I leave outside with no problems, and even have experimented with leaves low to the ground that have survived multiple winters now, but I do not recommend it.)

Cleaning

Leaves that are placed indoors can be dusted or rinsed off. Given the rough surface of most leaves, I recommend using a duster that won't leave fibers on the concrete, or a damp cloth.

For leaves that are placed outdoors, I recommend rinsing them off very regularly (each time you water plants) to avoid dirt/sand/grime/pollen from accumulating in the veins of the leaves. This grime is often rough and if allowed to accumulate, it will start "sanding" the paint coatings of the leaf

To Seal or not to seal

Many leaves have a protective coating using a concrete sealer, which helps protect the leaf from fading. Over time this coating may wear, and it can be reapplied according to manufacturing instructions. You can find concrete sealers at the hardware store. If you choose to apply such a sealer, please take all recommended precautions to protect your safety. You can also apply sealers you find in the paint aisle of Michaels, which are often easier to apply and more affordable.

Note that the application of the sealant changes the look of a leaf (from matt to glossier). This sealant is not strictly necessary, and I leave many of my leaves unsealed because I sometimes prefer the more natural look.  If you purchased an unsealed leaf and prefer the glossier wet-look, go ahead and apply a sealant! 

Fixing Damage

If you accidentally damage a small piece of your leaf (either in transit, or by dropping it) I recommend using a small amount of outdoor acrylic paint to paint the exposed concrete. You can get a variety of colors at for example Michaels Stores for about $2-4 a bottle.  For more detailed repair including  reshaping your leaf (for example if the tip of a cup plant leaf broke off), you could use a Dremel with diamond bit to grind the edge until you have a new (aritificial) tip, and then paint the result.

Coaster Care

For concrete coasters, gentle handwash only.
All coasters have a cork bottom.