Trust me, there's no rush to do missions and start choosing sides just yet, it'll only throw you in head first and get you in the habit of grinding, which is never fun.

Once the trails all over and done with (it continues through past a building with an exile contact and across into your first dungeon btw, introducing some more under appreciated game mechanics.) then feel free to start your missions using your phone menu. However, once you reach the stage the system just starts generating "Standard" missions, take a step back and take a look at what are called Archive Missions. Standards are a horrible grind trap and generally pretty useless after you've got 50 reputation points anyway. Archives give more exp, tell you the past story from all 3 sides without negative effects and are all round more entertaining. By all means do some standards here and there to work on your rep but by no means start thinking they're the only content around. There's dungeons, collectors, exile contacts, access node and hardline hunting and come lv30+ a ton of quest content too.

Well thats my main piece of advice to ya but if you're on the Syntax server feel free to add "CloudWolf" to your buddies list and shoot me a tell whenever I'm online, I'd be more than happy to help.