How you approach trading will have a great impact on whether or not you make money. If you approach it professionally and treat it like you would any other business, you will be successful. It is amazing how people who are successful in other professions don't treat trading the way they treat their other business. Instead they start trading without enough knowledge or even worse, they rely on a stockbroker or other financial advisor to "handle" their money. Now who do you think will take care of your money better, you or a financial advisor?
To approach it professionally like a business, you must do the things that you would need to do in any other business to be successful. You would have to put the time and effort into learning the business. If you were doing it full time, you would have to put in a minimum of an 8 hour work day. You would have to work/trade 5 days a week. You would have to read industry magazines and newsletters. You would have to read books on the subject. You would go to industry conferences. You would have to be properly capitalized. You would have a written business plan.
As a part time trader you would have to do many of the things a full time trader does but you would probably do them on a lesser scale since you are spending the majority of your time at your other profession.