In Singapore, matters relating to wills are governed by the Wills Act.
Comply with formalities
To ensure that your will is valid, you would have to make sure that it complies with the formalities listed in the Wills Act.
Namely, (1) the will must be in writing. (2)You must be at least 21 years old. (3)You must sign at the foot of the will. (4)The signing of the will must be witnessed by 2 or more individuals and they must sign in your presence. (5) The two main witnesses must not be beneficiaries in the will, ie they cannot receive any of your properties should you pass on or you cannot distribute your assets to them.
Since the formalities of making a will may be onerous, you may want to engage a lawyer to help you.
Depositing your will at the Will’s Registry
The Will’s registry is a confidential registry where you or your solicitors can deposit information on wills. Even though it is not a must to register your will, you are encouraged to do so, especially if you have made more than one will, as this would signal which is the most recent will and thus ensure that your intentions would be executed.