Some more tips on Borderlands are below. These tips are more specific and do not fall under the basic tips guide.
Again I would like to thank Kad.
They are a little bit all over the place but that does not mean that they are not very helpful.
-There are 160 missions total. 30 are main plot Missions, completing these will beat the game.
-In New Haven there is a secret weapons vendor across from the weapons vendor that is already there it opens after you have killed Krom and it will be almost directly behind you when standing in front of the weapons vendor. The weapons are generally better.
-In the second play through you can do the claptrap missions again. If you get a grenade mod as a reward reload and do it again until you get a backpack mod. Its a small chance but it is well worth it.
-Item drops are completely random but the more players you have in the game the better the equipment this includes stores.
-Don't waste your time looting chests and reloading the game. Killing end game beasts are way more effective and net you valuable proficiency experience. So loot wherever you want but then kill the last area enemies.
-Don't waste your time power leveling unless you have already beat the game. Not only does it take away from the fun but it is worthless because your weapons will still suck for your level and you will die and lose more money than you would if you were at the right level. Only power level if you have maxed out a char and want to play with the other chars. Cause then you can skim through the plot missions and get better weapons faster.
-Old Haven, Trash Coast and The Promontory are the best places for looting. Trash Coast is only good on your way to the hive otherwise get the fuck out unless your killing the mini bosses too for quest items on the second play through after you beat it.
-From the last tip. If you beat the second play through then you can go back and kill the bosses for the quest items you would have received. E.g. kill scar for T.K.s wave with a small chance of scar dropping it at a level 48 cap.
-Don't waste time pondering weapon choices and don't hold onto higher level weapons. The weapon you have been using for a while is usually just fine. At least you know what it does and many others that are better than it will soon fall too your feet. Then start nitpicking sell the weapons for money. Don't waste your money on anything with one really good exception and that is you haven't seen anything better in like 4 hours of game play. Unless its a shield or class mod they are so hard to find. Trust me you need serious money to buy the last level ammo upgrades and they are totally worth it.
-Many quest items will carry you through much of the game. For example a hunter using the elephant gun can go very far if he has the sniper upgrades. If you have it you should just use it and save the money. In the example above you don't have a scope but does it really matter if you one shot kill everything.
-Look at all the stats before you invest in a single tree. If you invest in a stat it is better to max it out. For example the soldier class has a refire skill which every 2 seconds will remove 1 second from the cooldown of your turret at level 1. At Level 5 its 5 seconds. Pretty good when combined with the level 5 cooldown reduction skill which reduce the cooldown time of the turret by 100% making it only 50 seconds instead of 100 seconds to throw it out. The two skill are in different trees but combining them makes a powerful duo causing your turret to comes out maybe every 20 seconds in a fire fight. I think that's pretty good.
There is some more tips and guides for Borderlands
Basic Tips Guide
How to - Bosses