You can earn your way to a free flight within your first 90 days by meeting the spending requirement for the signup bonus, which will award you with a nice chunk of miles. (cardrates.com)
There are cards that offer $ 500 and even cards that offer up to 100,000 points after meeting spending requirements. (rewardexpert.com)
You should be able to meet spending requirements on reward cards without increasing your overall spending. (magnifymoney.com)