@Bruce Lynn Is one of the key guys here for his knowledge on TX tax sales.
Although I do not deal in TX what he say is pretty typical of tax sales today. Remember these are auctions, so there will be experienced people who know how to play the game very well bidding against you. It is much more competitive and therefore not as profitable and more risky than those selling books imply.
That is not to say you shouldn't try, just be prepared with realistic expenctaions. Often a good place to learn is the county websites that often have information about the sale and the rules. 'Ther are three things to be aware of
1) The rules and laws and how they might affect your profitabiity (including hidden costs)
2) Exactly what are you bidding on.. SOmetimes the descriptions can be hard to understand or even be misleading
3) The true as is value of what you are bidding on. The assesed value or a Zillow etc estimate of value is not good enough