I joined XBox Live the day after Halo 2 came out, I've played each release religiously, and I'd say I'm fairly competent at the game.
But can someone explain to me (like I'm five) how to properly use the Battle Rifle? I stayed away from it in every single game because I'm so awful with it.
1. Try different sensitivity settings for your controller then practice with what you feel comfortable with using in close and long range battles.
2. Use the left (strafe) thumbstick to aim more than the right (look) thumbstick. Strafing to dodge and aim simultaneously is ideal.
3. Keep your first few shots on the body or neck then aim directly for the head as their shields pop.
4. Use teamwork, stick with someone who is BR/DMR'ing as well and learn to team shoot.
5. Use more teamwork by listening to teammates callout enemies thus giving you the first drop advantage.
6. Use cover to pop in and out during a firefight, don't just fight in the open.
7. Look for your your teammates red death X and most likely you can BR/DMR to finish and enemy or two. Having the shield advantage will help you win BR/DMR battles more.
8. Learn what range you're good with the BR/DMR, for close quarters don't use the Br/DMR unless you get a grenade advantage.
9. Use grenades to deplete enemy shields then it's just one headshot from your BR/DMR for the kill.
10. If it's Halo 3 then you need to lead your shots by about 1/3 or 1/2 of a head width.
11. If it's Halo Reach then don't lead your shots.
12. Don't always stay in the fight. If you're losing and know you're going to die then run away, pop back into cover and give shields time to recharge so you can attack again when it's more advantageous.
There are many finer points but this will help improve your BR/DMR game.