For the most part, proving residency is as simple as signing an affidavit which indicates when you moved to Texas. There are situations however, such as when someone contests your claim, when you may be required by the court to produce further proof.
Acceptable evidence may include things like a lease, a copy of your utility bill or even mail with a dated postmark to prove when you began receiving mail. Any of these things can be used to help prove residence if needed.