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Here is a nice summary on steps to take to enforce your judgment: https://www.traviscountytx.gov/justices-of-peace/jp1/collecting-judgement
For more detail, I would recommend this publication: http://images.jw.com/com/publications/433.pdf (includes strategies and tips which may be helpful if you have trouble tracking down your debtor's assets, etc.).
The basics are:
The debtor may have some protections against these remedies (such as the "homestead protection" for certain property, and limitations on how much you can garnish at a time), but it is the debtor's duty to raise these protections.