Set a certain amount of money aside every time you get paid. Put this in a difficult-to-access account. This will eliminate the common excuse of not being able to afford to go; flights are expensive, but if you have the money you won't be able to procrastinate anymore.
Research where you want to go. "Overseas" is a vague destination, and is easy delay. "Vietnam in March," on the other hand, is specific and harder to put off because it's so concrete.
Set a date. This doesn't have to be exact, but it should be down to the month. Again, this will make your goal clearer.
Acquire a TEFL certificate. Not all language schools require these, but they will almost always make you more attractive, which means you can work for better schools and demand higher pay. In many Vietnamese schools, for example, TEFL-certified teachers make $16 an hour while those without made $14 an hour. Since an online TEFL costs around $800, you only need to work 400 hours, or 10 full weeks, to make your money back.
Quit your job and apply at a temp agency. Most temp agencies can give you consistent work, provided you are well-presented and meet the employment minimums of turning up on time and getting along with people. Temp agencies are easier to leave, thus making it easier to stop procrastinating.
Buy a plane ticket for the trip. This will force you to board a plane on a specific date, as to do otherwise will be costly.