How do I become numbered with His people?

In order for a Gentile to be numbered among His people (His sheep), that Gentile must be righteous, be Baptized, and be filled with the Holy Ghost.

from Third Nephi, https://scriptures.info/scriptures/bofm/3nephi/14

.. turn all ye Gentiles from your wicked ways and repent...

.. come unto me, and be baptized in my name, that ye may receive a remission of your sins, and be filled with the Holy Ghost, that ye may be numbered with my people who are of the House of Israel.

1.  stop being wicked

2.  repent

3.  be Baptized in His name

4.  be filled with the Holy Ghost

On the third of February, in a post titled "Baptism of Fire, I explored what "being filled with the Holy Ghost" really means.  

In order for someone to be "filled with the Holy Ghost" effort is required, in addition to following guidance received from Jesus.

To be filled with the Holy Ghost, also known as receiving the "Baptism of Fire", means to have your spirit cleansed and sanctified by God.  The process for cleansing your spirit is similar to the process of washing your body clean in the waters of Baptism.

Mormon repeats the same instruction, during his farewell address, in Mormon chapter three, end of verse five:  

"... and if it so be that ye believe in Christ, and are baptized, first with water, then with fire and with the Holy Ghost, following the example of our Savior, according to that which he hath commanded us, it shall be well with you in the day of judgement.  Amen".

https://scriptures.info/scriptures/bofm/mormon/3

earnestmormon.com