This is the time to plant your trees. Everybody is familiar with our large, beautiful pecan trees, but there are other native trees that make great yard trees in Central Texas. First you need to know what kind of soil you have. Is it sandy or blackland clay? If it is sandy, it is almost certainly acidic soil which measures low on the pH scale of .7 or below. Think of vinegar. This is sour dirt. If it is Blackland with a caliche shelf, it has a basic pH. Caliche is sedimentary rock that is made by the deposits of the shells of ancient sea creatures, therefore it is preliminary limestone, and easily dissolved by running water or acid rain. This makes your water very hard, and it leaves limestone deposits everywhere it dries. Limestone causes your water to be full of calcium, and it is very basic or high on the pH scale .8 or above. Think of baking soda. This is bitter dirt.
Now most plants like sweet dirt. This is dirt that is full of organic matter and is just a tiny more basic than 0.7 neutral. Anything around .65 to .75 is considered good dirt for most plants. Some plants don't care so much, other plants care a lot. The best advice I can give you on picking out something to grow that will do well for you is to consider several things. First: what is the pH of your soil and does the plant care? Second: is the plant adapted for your climate zone, and availability of water? Central Texas is right on the edge of zone 8, but the hill country has a higher elevation, and it is in zone 7. Zone 7 will have colder winters with frost dates arriving earlier.
After you consider these things, find out if the plant grows best in sun, partial shade, or full shade? Google is quick to use to find out about the plant in which you are interested, otherwise you'll need a lot of gardening books. Now you are ready to pick out your trees. Many people want a quick shade tree. They are tired of the hot sun beating down upon their house. The problem is, the quicker the trees grow, the less long lived it is. Willow, Arizona Ash, and Hackberry trees grow into large shady trees very quickly, but they will begin to die after 25 years, maybe sooner. Perhaps you won't be there to care, but someone will certainly be cursing you when they have to pay a lot of money to cut down a very large dying tree next to your house.
My advice is to plant your trees out away from your house, preferably on the southwest side so you can have nice shade somewhere in the yard. As the sun goes down, the tree will cast your house in the shade without it being too near, and build a porch to shade your south and western windows or plant a tall shrub in front of them, if you don't intend to look out very much, then put a light colored roof on your house to reflect the heat. It's rather dumb to put a black roof on your house in this climate. Everybody's worried about mold showing. Mold will not hurt your roof, but a black roof will absorb a tremendous amount of unwanted heat in your attic space. Even vents won't help too much when the high temperatures hovers around 110 F for days on end.
So now you have decided you want a nice big shade tree somewhere away from the house. If you aren't going to live there too long, and you need quick shade consider Arizona Ash or the lowly Hackberry tree. Both of these quickly grow into very large, spreading shade trees of about 75 feet tall. If you don't mind nuts and sap falling on your car, plant a pecan or black walnut tree. Both make a very large tree with dense shade. The black walnut tree has larger, messier nuts with a green husk that rots off, but has denser shade, and a rounder shape. All of these trees have a tap root, which is why they do well in deep soil and can usually find a crack in the caliche to penetrate the deep soil below to find water. Many times the caliche is nothing more than a shelf of gravel and rock several feet thick. When you plant your trees, it helps them a lot to break open the caliche with a sledge hammer if you can. This is hard work, but better than planting lots of stuff that never seem to grow.
If you want to plant long lived trees with dense shade there is always the evergreen live oak tree for which the south is famous. These trees grow so slowly, you probably won't be alive when it becomes really large, but if you have the room, plant some for posterity anyway. Other choices are the other oaks. There are many oaks that do well here, red, white, shumard, pin, burr, etc. The nice thing about these large trees is that they are deciduous and lose their leaves in the winter to let the sun shine on your house. If I let the sun shine into my storm door, I hardly need to use our furnace on cold days, and it really saves on the heat bill.
Now, you have picked out your large shade tree. What if you have a small yard or want to plant some smaller trees that not only give shade, but also are ornamental. There are many nice ornamental yard trees you could grow. One of my favorites is the Mexican redbud. It does better in alkaline soil with less water needs than the Eastern redbud. There is always the crepe myrtle. It has such pretty bark if you trim off the lower branches and has a very long colorful bloom season in the summer when little else is blooming. Some other small flowering trees you might not be as familiar with are the Mexican buckeye, Anacacho orchid, and the red buckeye.