I want to apply for a Masters degree but have a low average, what can I do?
This really depends on how "low" your GPA really is. Generally universities require a GPA of 3.0 or higher. However, many universities will also accept students who have an average of 3.0 or higher for their final 60 credits (or final two years). Depending on how important this is to you, you can do the following:


Enroll in related undergraduate classes at an accredited institute and get good grades. Many schools will consider your total undergraduate GPA from all institutions you have attended (despite the fact that you already had an undergrad degree). I've known of people successfully doing this.
Get a short course-based master's degree at a smaller university with lax admission requirements and try to get a high GPA. After graduating you can try to get into a better school with higher admission requirements. I had a cousin who did this and moved on to get a graduate degree from a highly reputable university.


Both of these obviously require you to spend considerable money and time (a year or more) on this.