The lights are on
Borderlands is a FPS, that's a given. But playing it like a Doom-esque FPS will get you killed fast, especially because your enemies seem as if they are stronger than you no matter what. Well, here are some helpful hints to ensure that you stay alive on Pandora long enough to loot that chest over there.
-It may seem obvious, but using cover is key to staying alive and making sure your shields stay up. If you're in a heavy firefight, find a good spot to sit behind so that you can get shots out, but retreat if your shields are depleted. You will be shot (a lot), and your shields will go down, but keep them up and you can fight your way through any situation.
Keep your shields up!
-As stated (numerous times) in the above section, your shields will become your best friend. Make sure they are fully charged! As long as the enemies can't chip away at your health, you will persevere. Stay behind cover, get a few shots out, and go back to let your shields recharge. Any fight can be won as long as the enemies shoot out your shields instead of your health.
Find a health regenerating shield!
-Health doesn't regenerate in this game (sorry CoD players), so finding a health regeneration shield will remove most of the hassle of using potions in this game. There is usually one at the first Dr. Zed vending machine you come upon (the one you fix), but the problem is it's pretty expensive. You'll be able to find one easy enough in the later levels, but it's a good idea to try to get one as soon as possible.
Kill whenever you can!
-You can gain a lot of XP by just doing the quests alone, but you can even more by completing the challenges (you can find them under the quests tab in the menu). Killing all enemies will not only get you closer to the 'kill about a million enemies' challenge, they will also give you a fair amount of XP themselves. Try to memorize enemy spawns (skag spawns are easy, just look for the burrows), because they respawn eventually after you kill them. I recommend checking for enemies after a few quests, to ensure that you have a steady stream of XP coming your way.
Screw the classes!
-Just because you chose the Berserker doesn't mean you can't use a SMG, Shotgun, or Sniper. Don't think you've been shoehorned into using a particular weapon based on your class. Use whatever you prefer. It may not seem like good advice, but comfort in your weapons means comfort on the battlefield.
Find what suits you!
-While playing the game I came upon a sniper rifle that was insanely powerful, but was ludicrously slow and inaccurate. After that, I used only rifles that had a high rate of fire and excellent accuracy. What I'm trying to say is that people have different preferences. Don't use the guns that your friend uses, experiment with many different guns to see what suits you. Try guns that have varying levels of fire rate, accuracy, and strength, and see what you'd rather have in your guns. As stated before, comfort in your guns means comfort on the battlefield.
-You get more XP while playing online, so if you have internet connection (of course you would, why else would you buy this game?), go online and find a game of 3, join 'em, and blast everything in sight. Do this especially if you're a low level: join a higher level game, and if they don't kick you out (which they probably will), just hang back and let them do all the killing. You gain XP from slain enemies whether or not you helped in its slaying. You also gain a share of money whenever someone picks it up, so it's also a good way to gain a considerable sum of cash for yourself.
Aim for the head!
-Is not a good idea 100% of the time. Learn the weaknesses for all the different types of enemies. A skag's weak spot is their mouth. Wait for them to yawn or roar, and blast 'em. I suggest a shotgun for skags. Bandits' weak spots are, obviously, their heads. So the only time my title for this section would work is against a bandit. Some enemies, like the scythid, doesn't have a weak spot, so it's just a good idea to fill them with lead.
Use your special!
-The special changes for the different classes, such as a turret for Roland, and a rage mode for Brick. Learn to utilize their specials correctly and under the right conditions. The turret is good for distracting enemies and mowing down weaker enemies. The Berserk mode is perfect for bigger enemies (especially if you added an elemental artifact), but it's easy to get disoriented in the middle of a fray. Lilith's Phase Walk is best used as an escape if you get caught between enemies, but it is also good for weakening the enemies around you. Bloodwing is one special I haven't had enough experience with, so I don't have anything to add now.
Hopefully these tips will keep you alive a little longer in Pandora. Keep lootin'!