1. Be fast on the BA pick. Not only do you get more kills which look good on paper, but being able to quickly acquire and hit a BA is good practice. If u can hit the little things, big mechs will be no problem at all.
2. Know the best parts to hit to neutralize your opponent. No point in absorbing tons of dammage as you aim for their CT or head if you can be knocking out the very weaponry that's damaging you.
3. Be able to hit at range. It's easy with lasers, but with projectile weaponry it may take some getting used to
4. Know how much damage your weaponry does. You may be able to take a pot shot off at a more damaged opponent off in the distance and eliminate him before focusing all your attention on the brand spanking new mech right in front of you. In other words: Choose your targets wisely.
5. Avoid using missiles. They're easy to use, and take no practice. Early in game, they're generally used more close range. Not only do they do adequate damage, not only are they easy, but the give significant knock around on your opponent, thus screwing up their aim. Tactically a grand idea, but not so much if you really want to get better.
Infinity and beyond (for now): But let's be honest, to get those 30-1 "above average"kdr's and scores, grab a missile boat and sit in the back. That's generally the "key" to high score/kd. I do not endorse this as it is skilless. So you're not really getting better at the game, you're just using an easy tactic to win big. But that's just imho.