I'm sure there are hundred of guides to the game, some more concretes over a certain topic, while others might go through different topics. This one, will be one more but I hope it brings some help to some.
First and foremost, I'm trying to consider this guide for those that opt to play the game as Free to Play.
First thing to be aware are the main differences between each type of profile in the game. There are three profiles, Free-to-Play, Prefered Status and Subscription. The last one we don't need to discuss it, that's the normal profile for those that pay the subscription every month. They will gain each month also 500 Cartel coins that they can spend on the ingame store.
The Prefered Status, is directed to those that previously made some expense over the game, either old time subscribers, or someone who spent some money on the Cartel Store. They will get 6 character slots, 4 quick bars, and some other perks.
The last option, Free-to-Play, will be directed to those that haven't spent anything in the game, and will be reduced to 2 character slots, 2 quick bars and some other features will be non-available.
A more detailed version can be seen
here.
The Free-to-Play model is a bit restrictive, but I think it's possible to level from 1 to 50. In any case my advice would be at least to pick the Prefered Status. It's 5 euros, which will give 450 cartel coins, that you can use to purchase some small perks.
Leveling
Being a Free-to-Play player, carries a few burdens. The most notorious, is the reduced amount of experience gained, and the fact that you can't stack rested experience. As a result, leveling will be longer than a subscriber (note that this also affects players with Prefered Status). As leveling comes, while questing, there is nothing a Free to Play player won't have access. The quests are the same, the planets are all the same, nothing is blocked.
The current path from each faction, planet wise is the following:
Starting Planets
Korriban (Sith Inquisitor and Sith Warrior) and Hutta (Imperial Agent and Bounty Hunter). This will be the starting ground for each player. Here you will be introduced to the game, will start your class story and you will get your first companion. These companions will prove very useful while leveling. Progression will go from level 1 to 10 on average. Also when you finish the planet this will mark the end of act one, and as a final reward you may choose your class advancement. Sith Inquisitor will branch into Sith Sorcerer (Range Damage or Healer) and Sith Assassin (Melee Damage or Melee Tank) while the Warrior will branch into Marauder (Melee Damage) or Juggernaut (Melee Damage or Melee Tank). For the Imperial Agent it will branch to Sniper (Range Damage) and Operative (Melee and Stealth combat or Healer). The Bounty Hunter divides into Powertech (Range Tank or Range Damage with some melee abilities) or Mercenary (Range Damage or Healer).
Also here you will be able to pick your crew skills for the first time, after you finish the planet.
Level 10-16. The Capital Planet of the Empire. This will be the second planet, and probably the second longest, in terms of levels it lasts. Typically a quest planet, and when you finish you will have access to your personal spaceship.
Level 16-20. Just a regular level planet. Nothing major happens here. A mix of industrial, plains and mountains on this planet.
Level 20-24. Nar Shaddaa is an city planet, much like Coruscant, and with a high proliferation on crime. This will be the first planet you will actually see opposite faction. Yet another regular leveling planet.
Level 24-28. The first familiar planet, for most Star Wars fans. This desert planet offers players quests and first open world pvp area,
Outlaw's Den. To be fair, the only pvp I got there was back at the Rakghoul event, where we had to kill a champion enemy for the lore entry and title.
Level 28-32. Meet Alderaan before the Death Star blows it to pieces! (That will take place 3000 years later). Mostly snow, mountains and some green areas, this is the scenario for this planet. Another quest planet.
Level 32-36. Meet the Star Wars zombie version, Rakghoul. Taris is a dying planet, where plague and virus spreads. The Empire wants to finish the job. Quests here again.
Level 36-37. The smallest planet in the game. Questline is so fast here, when you think it's getting interesting, it's over.
Level 37-41. The frozen planet Hoth also makes an appearance over SWTOR. Longer questlines again, and a bigger planet than average. But mostly everything is frozen solid. Be sure to bring warm clothing. Was here I did my first world boss, more than a year ago.
Level 41-44. A prison homeworld. The worst of the galaxy are exiled here, and in some cases put in some isolation cells, for galaxy safety. You would expect the interest of the empire over this planet. You will have access to dailies when you reach 50, in Section X.
Level 44-47. Getting there. The mystical Voss are being fought over by the Empire and the Republic. Each faction is trying to prove they are the best ally. It's up to you to convince them.
Level 47-50. Finally you got there. The business world of Corellia will mark the end of your path to 50. Being a Republic planet, you will have to fight over this planet to make it fall to the Empire. There will be also dailies available on this planet, on Black Hole, when you reach 50.
Level 50. Ilum was suppose to be the open world planet for PVP. But due to bugs and issues with it, Bioware end up to take away the PVP features for this planet. Still this planet offers some daily quest activities.
The difference between factions, over planets, lies at the first 20 levels.
Level 1-10. Tython is the home planet of the Jedis, Knight and Consular, while on Old Mantell will be hosting the Smuggler and the Trooper.It works similarly to the Empire version, with the same ideas to companions and class specializations. So for a Jedi Knight, he can opt between Guardian (Melee Damage or Tank) and Sentinel (Melee Damage). The Consular either picks the Sage (Range Damage or Healer) or Shadow (Melee damage or Tank). The Trooper specializes either on Vanguard (Range Tank or Range Damage with some melee abilities) or Commando (Healer or Range Damage with some melee abilities). Finally the Smuggler can either be the Scoundrel (Healer or Close Range Damage) or the Gunslinger (Long Range Damage). Overall the classes share similarities in how they operate for each faction.
Level 10-16. Coruscant is the Capital Planet for the Republic. And as much as the Empire side, by the end of the planet, the players will have access to their personal spaceship.
From here on things are almost similar to each faction, except for Taris and Balmorra. While the Empire plays on Balmorra from 16 to 20, the Republic will only come here at level 32, and the reverse situation happens for the Republic. Taris is level 16 to 20 for the Republic and Balmorra is level 32-36. Of course each planet quest line will adapt to the current faction. So you might be fighting over a planet on one faction, and defending it if you do it with the opposite faction. Let it be noted, my highest Republic is character is on its level ~20.
Note: due to the fact that the in-game quest helper is so effective, I felt it wasn't necessary to post any information on the quests themselves.
The path to 50 is always the same for all classes. But for instance, if you feel too bored of repeating everything over and over again, there are alternatives ways of leveling. Flashpoints is one idea, another is doing space missions and probably the best is joining PVP. It won't net you more experience than questing but it's a different approach. In any case, you will always need to do planets to progress at least your class quest. I do know, however, that some activities are reduced, like doing Flashpoints for 3 a week or Warzones for 5 a week, for F2P. There are passes for that, but for a new player they are expensive.
Be also aware that on each planet, class quest line will reward you differently. So you may end up getting, lets say a new companion sooner with one class then with another one.
As I said before, a F2P player will get less experience as a subscriber. I can give you as an example, when you finish Dromund Kaas, you will be averagely a level lower than a subscriber (I've tried that). My advice is, if you can get, get the experience boosters whenever possible, either for PVP or Flashpoints, which are cheaper in the GTN, or if you can afford get the boosters for normal quests. Probably as a first character it will be impossible for you to buy them at the GTN, but for a second and third character this is possible. Also, every heroic quest in game, is repeatable in a daily basis, so if you can do them often.
My take would be level maybe one character to 50. Don't focus too much on lots of different alts at the start, unless you are looking for the class the suits your gameplay style. Only now did I got a second character to 50, almost a year after I got the first one. It's true I was absent of the game for some time, and it's possible that I won't have another 50 anytime soon, but if you focus too much on several characters at the same time, it might burn you out.
In resume, pick a class you would like to play, focus on it, enjoy the storyline (specially your class story), don't rush it, join any group activity (you will see on every planet people asking members for heroic quests), try different builds and learn the ropes of the game. Again, don't rush it. Rushing a game it's what ruins them. Personal opinion, tanking as a Powertech is really fun.