Ok guys, first of all bad company is an offline and online game but now, I am going to be talking about online skills and how to do things. If you think you are awesome, become better here.
Aiming: You can aim by pressing L1. It's always better to aim then just shoot at someone, especially on hardcore. This unless you are really close that person then you don't want to take the time to aim or you be the prey, and fail. A lot of people I know always just shoot but that's bad because, one, blows your cover, two, if your fighting a group it's likely you get killed or die with only one death, aiming helps there because you kill one quickly then take your cover.
Accuracy and sharp shooting smarts: If your the type of person who loves to either snipe, use a rifle (M1 garand, or M14) then being accurate has to be one of your skills. When you are aiming, don't open fire without a clear shot and COVER. If you don't follow those tips you are likely to be counter sniped. It's never a good thing to die.
Decision making for weapons: When you are choosing a weapon, think about the battlefield and you opponents. If you are in open cover map then not a good idea for a sniper, less cover and hiding is not a time to be sniping and sharp shooting. Instead a better choice is an Assault kit. For accuracy from a far and quick reloading. The best times for medics are when bullets are flying everywhere and all you can do is keep firing and hope you get someone. Engineers are only useful in close range combat and against vehicles. Snipers out there, save mortar when a tank is standing still.
Ever get tired of dying when you encounter a group? Well here it is, Solo tips: Best to always have a squad, though they aren't always online are they? This will help. Learn to make a habit of throwing grenades into a house. Always be alert and find cover. Be your own one man army. When you encounter someone first shot is one of your only options, don't switch to your better weapon and always reload, don't want to reload in the middle of fighting right? Then reload!
"dude?! Use the CHOPPER!!!" "uhmm okay" *fly fly CRASH. Helicopter tips: First, get used to how it is, hard to fly one! Make a habit of jumping before crashing then double tap "X" for a parachute! Now, flying one, yikes scary huh? Well get to a great height/altitude and practice up there. Whenever you go forward keep pressing the ascend button. Don't be selfish. The chopper is for everyone.