Determine whether your state recognizes self-proving wills. Check the laws of your state or ask your lawyer whether your state has a statute recognizing self-proving wills. If your state does not recognize self-proving wills, it is even more important that you verify the formalities required for making a valid will.
Execute affidavits according to state law. If your state recognizes self-proving wills, there will likely be statutory requirements. Generally, to make a will into a self-proving will, you must have two witnesses sign the will and execute separate affidavits that must be notarized.
Insert a no-contest clause by adding language to your will that states that anyone who is entitled to receive under the will forfeits his gift if he contests the will. While this won't necessarily prevent a contest, it will raise the stakes of the decision, making it much less likely.
Update your will if you move or change your marital status. If your will was executed in a state other than where you currently live, or if you've subsequently been married or divorced, there is the possibility that your will won't be recognized in the probate court of your current state. Avoid such a contest to your will's validity by updating and possibly re-executing your will when you change states or marital status.
Avoid the appearance of undue influence. If you're choosing to leave most of your estate to a select group of beneficiaries, avoid the appearance of undue influence by being open about your choice. Explain your decision to your lawyer and other beneficiaries in rational terms to make a contest less likely to be effective.
Choose credible witnesses likely to outlive you. If your state does not recognize self-proving wills, your choice of witnesses could become significant. Credible witnesses that do not have criminal records and who will likely be able to be found after your death will make it difficult to contest the validity of your will.
Clearly revoke prior wills. Each time you execute a new will, be sure it expressly revokes all prior wills. If possible, also destroy all copies of previous wills. If more than one will is in existence, there is a greater likelihood of a contest to your last will's validity, particularly if there is a significant difference in the way each disposes of your estate.