Assure yourself that you have standing to bring a will contest in your state. Most states require that a person challenging a will be an heir under the current or a prior will. Review your copy of the will carefully. In order to make a valid will, the testator must be of age and sound mind when she signs it. She must know that she is making a last testament and exercise her own free will in doing so. She must also execute the will according to state law. Consider any facts or evidence that suggest that any of these will prerequisites were not met.
Consider whether the testator was of age and of sound mind. In most states, the legal age is 18 or older, but several states allow younger testators. If the testator was not of proper age, the court will invalidate the will forthwith. Courts interpret the "sound mind" requirement to mean that the testator must be capable of the same level of rational thinking as an average person. Courts presume that an adult is of sound mind so anyone alleging lack of mental capacity bears the burden of proof. Look for evidence that the testator took medication, was senile or suffered from mental illness at the time the will was signed.
Investigate whether the will represents the testator's own free will. This question is among the most frequently litigated in will contests. Evidence that someone tricked the testator into signing the will -- that is, evidence of deceit, fraud or forgery -- invalidates the will. Evidence that someone unduly influenced the testator also invalidates the testament, but the influence must rise to a level negating the testator's free will. Usually when a will contestant charges undue influence, the testator was feeble and the person influencing them was in a position of strength or confidence, such as the testator's doctor or caretaker. In many states, if one of the affirming witnesses is an heir under the will, the court presumes undue influence.
Consider whether the testator knew she was drafting a will. Generally the testator declares before witnesses that the document is her last will and testament, so check for witness names at the end of the will and -- if the situation warrants -- interview them. Talk to anyone else present at the will execution and also to medical staff treating the testator at that time. Next, look at the execution process and make sure it complied with state law. All states require that at least two disinterested adults witness a will -- people over 18 who are not named heirs in the will. Both witnesses must have either seen the testator sign the will or else heard the testator affirm her signature.
Present all evidence that the will is invalid to an attorney who prepares a will objection. Alternatively, research probate law and procedures in your state and prepare and file the objection yourself. The probate court assigns a trial date. Appear on the trial date and present your evidence. Convince the court that the will is invalid. The judge either rules from the bench after all parties finish argument or else she takes the matter under advisement and mails a decision some days later.