Yes, technically, you can. But there are some guidelines that you need to follow.
1. 4 basic clauses - revocation, domicile, executor/trustee, residuary
2. 2 witnesses who are non-beneficiaries

Any mistakes, and you end up partially intestate.

Keep in mind
1. Getting married invalidates a will.
2. Name legal guardians for your children.
3. The longevity of executor/trustee/beneficiary.
4. Have enough documents to prove your ownership of properties attached.
5. The bulk of the cost does not come with writing the will, but the execution.