Greetings to the new recruit.
let me clear a few things...
1.While aliens have much more HP, it doesnt necessarily mean much.
While a tyrant has 400hp, a Battlesuit, when the damage reduction is replaced as hp, has 250hp.
L. armour and a helm leaves you at 150hp.
2.One of the things about playing with the humans is teamwork.
Often, you will find there is a goon (short for 'dragoon'), or tyrant on the enemy team which is a excellent player - usually, this means that its almost impossible to kill the guy by yourself.
Basically, while I dont recommend saying "Someone accompany me", if I were you, if I see a fellow battlesuit/shotgunner/etc leaving the base, I would follow him. Now, if he runs into...'trouble', you will be there to help him, and will probably net the kill as he is killed.
3.The more expensive weapon is not always the best-
different weapons suit different playstyles.
I personally adore the shotgun and the flamer, but you will probably kind a fav weapon yourself soon.
Basically, the 'painsaw' deals 200dps, however is the cheapest weapon of them all. This makes it a excellent weapon for rushing bases, dretches, and 'that' goon who hasnt noticed you.
The shotgun, at roughly 56 damage per shot and 150 credits, can often be more useful than a lasgun at 250credits.
Infact, the free rifle is sometimes more useful than a lasgun, however the lasgun too has many perks. What im trying to say is that dont pick a weapon based on its price. The only 'BFG' weapon here is the Luci (Lucifer Cannon) - at 250 damage for a full charged 10 unit shot, it can take down anything short of a tyrant in one shot. While it does have certain limitations, its safe to say its the 'best' weapon in the game as a overall 'uber l33t killz0r' weapon.
4.Try not to build unless you really do know how to. Watch how people build, then once oyu think you are ready, try it yourself.
5.Watch this
http://www.youtube.com/watch?v=doTBT46wMvAHeh heh heh - I laugh everytime I watch it