Start with how you'll use the space. A dining table and grill need more room than most people expect, so mark the outline on the ground and set out your furniture before deciding on dimensions.
Slope and drainage come next. A patio should fall gently away from the house so rainwater runs off instead of toward the foundation. In Houston's heavy storms, a patio that ponds water or drains toward the slab causes problems fast.
The base is what you don't see and what matters most. Clay soil moves, so the ground should be excavated, compacted, and topped with a proper base before the pour. Reinforcement and control joints help the slab handle movement without random cracks.
Finally, choose a finish. A broom finish is practical and slip-resistant; stamped or exposed-aggregate concrete adds texture and character. If you plan to add a pergola, outdoor kitchen, or cover later, tell your contractor now so footings and utilities can be planned in.