A few rambling things I wish I'd known when I started:
-As someone here pointed out to me, if your target gets a floating red skull above it, go run up and melee it (F key default) for double XP and a little burst of gore.
-Lots of logos are back inside winding caves or you may need to up to a higher elevation to reach them. Keep that in mind since the map is 2-D but the environments are anything but. Meaning, if you reach an icon indicating a logos, and there's nothing there, look up, look above, or look around for a way to reach low or high.
-Speaking of logos, logosatlas.com is definitely your friend if you find yourself getting stumped on them. If you're worried about spoiling things, at least look up the Logos that require you to have 2-4 other logos first before you can open the transparent door to them (saves a lot of frustration).
-Pay attention to what ammo works best on which kinds of targets. You'll figure it out soon enough but I can't tell you how many new players I've seen pouring non-EMP weapons into enemies that won't take a scratch if you don't use EMP stuff (just one example)
-If you're really impatient about leveling, then doing instances (preferably with people, but in many cases you can solo it OK) is key.
-Instance missions are given all over the place (within the instance, outside the instance, sometimes not even in the same general planet zone), and sometimes you turn in missions completed *in* the instance *outside* the instance.
-If you play on Pegasus, look me up so I can add you to our fledgling, tiny (3 members with a few alts) GT clan. I haven't given up on it, despite a couple invitations to other larger clans.
-The Eloh Temples? Oh gawd, don't even get me started. Visit tentonhammer.com and make use of their guide for that and just about any other complicated quest arc you get stuck on.