General Tips

Save Constantly

Make frequent saves and separate files for these saves throughout the game. You may be unhappy with the repercussions that have risen from a previous decision, so instead of carrying the weight of this miscalculated decision you can simply just load up the save file and redo it.

Pick a route and go for it

For reasons we will reveal later (as they are a major spoiler), you should stick to going full Paragon or full Renegade. You're going to need the extra dialogue options to accomplish certain objectives with greater ease. Plus, there's nothing to gain from being neutral.

Do all the optional assignments!

This holds true especially as you near the endgame. You would stand to benefit greatly from being an over-leveled powerhouse as well if you're going for certain Achievements.

There's more to the game than missions

Beyond the shooting and saving people from distress, there are also romances to pursue, planets to explore (and mine), and Codex entries to be filled. The galaxy needs saving, but no one is in any particular hurry.

Upgrade whenever you can

In particular max out weapons, like the submachine gun or assault rifle, to drop enemies in a couple shots. Upgrade the Normandy as soon as possible as well. Look into the Argus Scanner Array research project, as getting this will expedite your mineral-mining efforts. You also might want to upgrade your Probe capacity, which can be gotten from Thane once he's on your team.

Never run on an empty tank.

Perhaps the most important advice we can impart before you let loose on the game is: Always make sure your fuel and Probes are fully stocked before leaving any system. These resources are relatively inexpensive, but the real loss is missing out on a wealth of mineral resources in the event you run out of fuel or Probes.