You cannot always ask permission, of course. If you are shooting a street scene or a wide shot of a market, you can't run up to everyone and ask if it's OK. In general, people do not mind this sort of photography—it's only when they're singled out that they get uncomfortable. But not always. Be sensitive to the scene in your viewfinder. If people are getting nervous, ask permission or move on.
Make use of people to give your images life and scale. If the facade of a particular building appeals to you, the picture may be that much better if you show people walking in front of it. They will give it scale and also let viewers know what sorts of people live there, how they dress, and the like. An outdoor café may be more interesting crowded with people than empty.
If the instability of the freelance photographer’s way of life isn’t for you, you can always find a day job that involves traveling. Then you can go to lots of places, be paid for it through your job, and do travel photography in your spare time. Jobs like flight attendant, global salesperson, English teacher (or a spy!) are just several of many professions that let you visit your dream locations, without being too risky on the financial side.
For micro-stock, I have portfolios on a dozen different sites. However, I really only publish images on a regular basis to ShutterStock and iStock. Between my micro-stock sales, I have averaged about $250 a month on average. The best part of micro-stock for me is that it’s fairly residual and passive. I spend very little time on it, and it keeps coming month after month even if I stop working at it.
When you arrive at your destination, be open and try to take note of the first impressions—write them down if you have to. (A notebook is an essential accessory for a travel photographer.) When you see a place for the first time from the plane window, or when you drive around a bend and there it is, or as the ship nears some distant island—how do you feel? Where do your eyes go first? What do you notice about the place right away? A smell? The heat or cold? Blistering sunlight? Mysterious fog? A particular building or vista? The way people move? Their dress? Whatever it is, remember it. First impressions are invaluable sparks to creative interpretation, and by definition are not repeatable. You've seen the place in pictures, you've read about it. Now you're there, and all your senses can partake.
There's much more to becoming a travel photographer than exploring exotic destinations and clicking your shutter. Getting up at stupid-o-clock to catch the perfect sunrise, carrying a camera that’s heavier than four backpacks, skipping meals in the quest for perfect light, and missing out on the travel experience because you’re too busy taking photos, are just a few of the downsides. 

This was a really informative article Hillary :) Just wish I found it sooner because just a week ago I went to the Grand Canyon to snap some photos. I didn't have this article to help, but I found a similarly useful article that provided some kind of checklist of things to do before traveling. If anyone's interested, here's what helped me out before I went to the canyon: