Star Wars : The Old Republic has quite a few ways to level up. The traditional way of soloing quests and content is the most popular one, but you can also PvP, group and do group content or you can grind Space Missions from your ship. This is a great way to level and will award you with some of the best and fastest XP in the game. It’s kind of like powerleveling yourself.
You can use this method of leveling all the way to level 50, but you are going to miss out on all the content. So either do this on an alt if you want to experience all the content, or combine this way of leveling with the traditional way. Running a lot of space missions will be quite tedious , but it is one of the fastest ways to level. This method of leveling is also good to combine with leveling through PvP.