As much fun as all the content is throughout the game, your end goal will surely be reaching maximum level. I'm sure it's possible to get there without questing but you'll be missing out on experience, items, story, companion characters and your advanced class.

The quest givers will always have an empty triangle above their head. They could be people, terminals or just plain items on the ground. Pick up as many as you can since they typically overlap in a given sub-zone and you're going to be there anyway. When you need to turn in a quest, the icon will be the same triangle but this time filled in. It's a good idea to finish all the quest objectives in a given zone before turning them in, it will save time.

Unless you are grouped, avoid any Heroic quest. Though they have good rewards, they are incredibly difficult. If you can find a group though, it's worth the time. At this stage you should keep away from credits farming, let's level your jedi/sith first then back to credits.

Leveling Strategies
The simplest way to level up is through combat and that means dealing damage to your opponents. Every class does this pretty well, though some advanced classes are better equipped. There are some basic rules of thumb to keep in mind though.

-Use a tank companion. The healers don't heal enough and the damage ones don't do enough damage when compared to you. A tank will keep at least 1 enemy off your back at all times. If you plan on leveling as a tank, then a healer companion would probably work out.

-Use crowd control abilities. 95% of all combat is against 3-4 enemies and if you can subdue one for 30 seconds, it will keep you alive.

-Use Area Effect (AE) attacks against 3 or more enemies. Less enemies than that, and you lose effectiveness.

-Have Medic Packs on your hot bar in case of emergencies

-Attacks that are channeled can be shortened due to taking damage.

-Every advanced class can focus on dealing damage through skill trees. Damage builds are the most effective at leveling, and the ones suggested in this guide.

-If you want to use a different skill tree, you can reset your skill points in your capital city, for a fee
Use knockdowns and stuns. Anytime the enemy is on the ground, they aren't hitting you.

When considering particular tactics, it's important to remember that nearly all combat will be against groups of enemies. Enemies come in 4 main flavors. Weak, which can do down in 1-2 hits, regular which will take 4-5 hits each, strong (grey star) which are immune to some effects and use a wide assortment of abilities and finally, elite (gold star) who have a lot of hit points, use many abilities and will pose a large challenge to all players. Think of elites as mini-bosses, in that you will need to use every tool you have to beat them.

Most groups will be composed of 3-4 regular enemies, though from time to time you'll find a tough enemy within their ranks. If you have a tanking companion, it's a good idea to send them on the strongest enemy, the tough one if it's present, and personally deal with the regular enemies. Some classes will be weak in the AE abilities department until the 20s, so take one enemy down at a time. If your class has a stun, such as Whirlwind for Inquisitors, use that to start the fight on the tough enemy instead. Granted they do more damage and have more hitpoints but it's a recipe for disaster letting 4 people attack you at once rather than taking out the weaker ones first.

Once you do target the tough enemies, keep an eye on their ability bar and you'll often find that they are trying to channel a large attack. Use an interrupt at that point to stop them. You can also use a knockdown attack or a stun. Usually you'll only need to do this once per tough enemy.

If you encounter an elite enemy, things are a bit similar to a tough one, the main difference is their damage and hit points. If they come with friends, take them out first. Once it's just you and the elite, get ready to use an interrupt rotation. Many classes have multiple interrupt-type attacks. These are either straight interrupts, knockdown abilities or a stun. A Trooper for example has Cryo Grenade to stun, and if they go the Vanguard route, they also get Riot Strike to interrupt and Neural Surge as a second stun ability.

An interrupt rotation is the act of staggering your abilities to get the most out of them by using the available interrupt with the shortest cooldown. In the Vanguard example above, Cryo Grenade has a 60 second cooldown, Riot Strike is 8 seconds and Neural Surge is 45 seconds. You would use Riot Strike, Neural Surge, then Riot Strike again since its cooldown would be finished, then Cryo Grenade. If you didn't start with Riot Strike, odds are you would only be able to get 3 interrupts before being unable to stop the enemy. This rotation is key to successfully defeating any hard enemy and in 99% of the cases, it is a better decision to interrupt an enemy than to damage them.

Fast Leveling Tips
If your goal is to hit level 50 as fast as possible, here are some general guidelines to help you along the path. You will be skipping a lot of the content however, and therefore missing a lot of the fun stuff that BioWare has put in the game to make leveling more cohesive and interesting.

All combined, you can reach level 50 in under 80 hours. To compare, a standard play through could run you 150-200 hours - that's a lot of skipped dialogue.

-Dialogue can be skipped with the space bar

-When dialogue choices appear, hover over them to see the Light / Dark options

-Ignore heroic quests unless you are grouped and close-by

-Ignore planet bonus missions

-Missions you do complete should be your level or one above

-Ignore all crafting and mission skills until level 50

-If money is not a concern, ignore all crew skills, otherwise take 3 gathering skills

-Don't buy anything on the GTN, you can level to 50 on mission rewards alone

-Voss, Corellia and Ilum quests reward commendations for level 50 gear, be sure to take them

-When leaving a planet other than the last 3, spend all your commendations on gear you can use or mods that you resell for credits

-Collect all the bind points on a map and use your recall ability, it should be on cooldown often

-Ignore PvP content while leveling

-Ignore World Bosses

-Ignore Datacrons until level 50

-Ignore Flashpoints, you will see them all at level 50

-Your first mount is at level 25 and costs a bit more than 40K, get it once in the town on Tatooine