any written job offer should point out that employment is "at will" – for a sample, see “Job Offer Letter” in this book under “The A to Z of Personnel Policies”
an oral job offer should be matter-of-fact and to the point – skip the usual "feel-good" comments that sometimes get a company in trouble, such as "don't worry, if you work hard and follow all the rules, you'll always have a job with us" – even though the Texas Supreme Court has ruled that such comments do not by themselves destroy the presumption that employment is at will, it is possible to do just that with the wrong mix of circumstances
in an employment at will situation, the employer should express the compensation in terms of a weekly or biweekly pay period – annual salary offers have been held in certain cases to constitute a promise of at least one year's employment
the more unusual a pay method is, the more important it is to put it into writing – also, the pay agreement should be as clear as possible, since any claims under the Texas Payday Law will be based upon whatever the pay agreement says or seems to say