Ask Mr. Smarty Plants

Leucophyllum frutescens (Cenizo) makes an excellent foundaion plant. It is cold tolerant (though it may shed a few leaves when it is very cold) and should do just fine if planted in December. Two things to keep in mind though, this plant liikes it dry, it will will not do well in an area where it gets too much water, and, it needs sun, it can handle some shade, but not shade all day long.

In case moisture or shade are going to be a problen, here is a previous Mr. Smarty Plants answer that suggests other foundation plants suitable to central Texas.

As for planting tips, make sure you have a fertile soil with drainage characteristics suitable for you plant (you may need to amend with compost). Dig the holes larger than the root ball of the plant. Remove plants from their pots by manipulating the sides of the pots to loosen the soil from the roots. Never pull on the stems of plants to remove them as this might cause injury to the plant. If the plant is pot bound, you may want to cut and spread out some of the roots. Backfill the hole with some of the loose dirt, then position the plant so that the soil line from the pot is level with that of the ground. Use the remaining soil to fill the hole.