There are two ways to go about this. One, as an earlier poster said, is to pick a trip and work toward that goal. This is why people apply for several, sometimes up to a dozen, different cards.

The other thing you might be thinking is, "Hey, I do a lot of spending already; why not get some points, and figure out later what to do with them?" If that's your theory, you should get a more flexible credit card.

So, how does this play out in practice?

First, bear in mind that you could apply for several credit cards. I got into this over the summer and have applied for five cards since July, which is not a lot by most people's standards but is kind of a lot for me.

Second, if you don't want to apply for lots of cards, decide which of the two categories you're in. If you have a specific trip in mind, identify what card(s) get you there -- maybe a Hilton card for hotels and an AA card for airfare, or whatever. If you don't have a specific trip in mind, the best flexible cards, according to most people, would be the Chase Sapphire Preferred, the American Express Gold card, or the Starwood Preferred Guest Amex. All three of these cards transfer to several different airfare/hotel programs, so you can build up points and then decide where you want to spend them. The particulars will depend on your situation. Chase Sapphire, for example, gives 2x points on dining, and I eat out a lot, so that's my preference. But the Amex gold gives you 3x points on travel and 2x on gas&groceries, which maybe optimal for you. Etc.

Once you identify the specific card(s) you want to apply for, do some research on here and figure out any tips, tricks, quirks, etc. For example, you can apply for two Citibank AA cards and still get the "first time applicant" bonus on each, if you apply for both on the same day. You can overcome a "denial" on a Chase card sometimes if you are willing to lower your credit limit on another Chase card. Etc.

Good luck!