It tends to take a while to earn enough air miles to earn a free flight. This is especially true if you gain most of your air miles from groceries and other small purchases. Obviously, you’ll earn points faster if you use your credit card on more expensive things.
Using your credit card while traveling will also help get you enough points in as short a time as possible. Overseas rates might be even better than your local ones. You should also take advantage of bonus miles earned from partner merchants.