They'll either make you or break you, all other things being equal.
Combat in Eve is about intel first, everything else second. But intel isn't worth much unless you can use it effectively to paint a detailed tactical picture with which to defeat your opponent.
Today was the first real day of actually trying to play Eve and PVP in over two months for me and the first thing I did was jump in blind into a fight with my Navy Mega and promptly lost it. I can count on one hand the number of Navy Megas I've lost in my entire Eve career and the number of BS kills I have using a Navy Mega are in the mid triple digits. The point being is that no matter how good you are, if you're not prepared with the proper intel, you're going to lose and lose big. I was lucky to get out with my pod.
When fighting from a static position (you're in your home system, targets are coming to you to attack you) success in battle is largely a game of chess. You know the enemy is out there, you know he's coming. The real question is where are his forces, what are they and how will they be applied? If you can understand these factors and have a firm handle on each of them then the outcome of the combat should already be predetermined- you're going to win, or you're not going to engage at all.
There are only two ways you can lose. The first is to be stupid and do what I did today and just jump into the middle of a fight with no intel. The second is where your attacker has done a skillful job of hiding his forces in such a way that you don't know one or more of the three aforementioned factors- size, composition or application, and you get pasted because of it.
It's *always* a trap. Always. Even when some annoying noob in a Scythe is mining in the bottom belt, it's a trap. What better cover for a scout than some idiot noob mining in a belt? Noob ships sitting on a gate doing nothing are obvious scouts. Some guy in a crap ship doing stupid things that noobs often do aren't so obvious, and just as useful as a scout. Word to the wise: kill *everything*. If it's not yours, blow it the hell up. The one time you don't is the one time it will cost you.
The FC's job is to stay calm and focused, even if the rest of the team isn't. Lose your cool and you've lost the fight. Losing isn't worthless unless you don't learn from it. If you keep repeating the same mistakes, then that's your fault, not someone else's. I know all of this sounds pretty obvious, but you'd be surprised at how often I see basic lack of application of these simple principles getting people killed (online, in internet spaceships). Then again, it gets people killed in real life as well, so it still applies.
When fighting from a dynamic position- you're the aggressor, the entry team, the guys jumping in with guns blazing- you can *never* afford to give the targets any time to acquire the size and composition of your force. Once you've decided to engage a target then commit 100%. Every second counts as it will give the defender more time to prepare. The defender isn't hiding. He's not scared of you. He's waiting, preparing, seeing if you'll make a mistake. As soon as the defender is alerted to your presence they're going to be optimising their forces and the battleground to engage you under the best possible circumstances- for them. You can't afford to be timid when on the offensive.
Don't engage when only half prepared. Everyone isn't in the gang yet? Everyone isn't fully informed of the plan of attack, target order etc? If not then you're not ready to fight. Trying to manage organizational issues while prosecuting a fight is a surefire way to lose. If you can't get organized in time, delay the fight until you can or withdraw to a more serviceable position. Consistently winning means being consistently prepared.