One of the things I've found helpful while leveling characters is the ability to switch world instances. World instances are the that Bioware handles lots of players on a given planet. Too many people and you get lag and too much competition for mobs, resources, etc.. By having from 1 to around 120 people per world instance Bioware balances the feeling of having enough folks around to make the world seem active with the easing of excess competition.
All that said, sometimes you hit the leveling wave at the wrong place on a planet and have to wait longer than you want for mobs, quest items, etc. What I've found that can sometimes help is to manually switch world instances (if you've ever joined a group on a world to do a heroic quest and been moved you've encountered the automatic version of this).
If you want to switch just press M to bring up the main map and look in the lower right corner at the World box. If you see your planet's name and a number then you're read to switch. If you don't see the dropdown box then you're currently out of luck as there aren't enough people on the planet at the time to spawn multiple world instances. I've only seen Quesh not have multiple world instances. (Mainly due to Quesh being so fast and short.)
Choose your destination, click yes, and hopefully you'll be able to get back to leveling!
Note: You can generally only take this option once every 30 minutes or so. Occasionally you can bounce between instances without having the cooldown start.