So I got to 35 yesterday on my Sith Warrior Marauder. (Shadow Hand, PvE, EST) And since their are currently a lack of guides around I thought I would post a bit about it.
1. The Marauder is highly gear dependent unlike the other classes. In order to hit like a truck you need the gear! End of story. There isnt a rotation but a priority. Balancing cooldowns and knowing when to use that 30 Rage on Beserk is key to doing consistent DPS. The Marauder is a complicated class to play, if I were to match it with a WoW counterpart it would be the Druid Feral Cat. I am currently using the Carnage spec and Quinn as my companion/ pocket healer. There isnt a group of mobs that I cannot take on.
2. Speaking of attacking packs, it is essential you prioritize your targets lest you find yourself dead. Rarely in SWTOR will you find single pulls or the rare lone person.
3. About Gear, and this is what I like about it from WoW, There is artifact gear (orange boarder) that have slots for mods/Enhancements/armoring; Find a look that you like and just stick the addons in it. If you get a nice quest reward that has current level slots in bust it up and place it in your armor! It will stay current with your level. The same thing applies to weapons and Lightsabers. (I got a cool looking Darth Tyranus-esqe saber early on and have pretty much kept it up to date by switching the mods for it.)
4. Questing, there are more than enough quests to level. I left Tatooine (5th planet in Sith progression: Starting planet, Dromand Kass, Balmora, Nar Shadaa, Tatooine, Alderann.....) yesterday with only about 1/3rd of it done. I was already over level for it!
5. Companions, use them! Keep them geared!
6. Datacrons, GO FIND THEM! They are permanent stat boosts for your toon. Also once you collect the shards theres a nice reward. (no I am not going to spoil it!)
Lastly lots of people have been asking me, "What should I play?" Well I will break down my observations also from the Sith side:
1. If you want to tank: (in order of my preference) Sith Inquisitor Assassin, Bounty Hunter, Sith Warrior Juggernaut
2. If you want to DPS: Sith Warrior Marauder, Bounty Hunter, Operative Sniper, Inq Assassin
3. If you want to Heal: Sith Inquisitor, Operative, Bounty Hunter