If you plan to attend a Phd program, graduate assistantship is the best way to earn an income and to decrease your expenses to minimum. During application to your program you will be asked if you are interested in assistantship positions.
If you are not clear about specific research area you are inetersted in, teaching assistantship will be your best bet.
The most important factors that will affect your chances of earning a teaching assistanship are your prior experience and your fluency in English. Therefore, you may need to take the TSE (Test for Spoken English).