If you have a horrible GPA, (like under a 3.0 or 2.7 or something like that) I have several suggestions:
1) retake many of the classes you made your lowest grades in, especially if they are common prerequisites. Getting a master's degree in something else might help demonstrate ability to complete graduate level work, but more likely would just put you in debt. I've also talked to OT admission departments that ignored all of my 3.8 GPA graduate work when calculating my "total" GPA.
2) get a huge number of OT observation hours plus some volunteer hours in areas related to the populations served by OT.
3) take several years and get a career in some other field. When you are older, some admission committees don't look at your undergraduate GPA as closely.
4) Become an occupational therapy assistant instead. If you could live with your parents, and take classes at a local community college, you could be out in 1.5 years while paying under $10,000. As opposed to $50-100,000 for many OT schools over the course of 2.5 years. You graduate sooner with less debt, and you would only make maybe $10,000 a year less ($6,000 less when you take taxes into account)