I find that I get a decent amount of kills and usually rank either 2nd or 3rd on my team, but get a ton of assists.  I'm not finishing off my enemies efficiently enough, and hence do tend to die a shitload. How do I get better at Reach, just bite my tongue and keep practicing? I've never played much Halo Online before so I'm sure I'm behind the curve compared to the Halo 2 & Halo 3 veterans.

Camp some more, it's basically the only effective in Halo. Thanks to the regenerating health system, the worst thing to happen to the gaming industry ever.

Shoot dudes, run up to them, melee them. Halo in a nutshell.

always go for headshots and pace your shots so that you cross hair bloom isn't fully expanded

Left Trigger will not help you aim better.

" Help here "

don't run into the same place you are being killed 
be witty  and use the enviornment to your advantage.  
learn to bounce grenades off of walls accurately  
make sure you don't abuse the sprint and always disable it when you see an enemy so you dont get killed while running 
short bursts with the AR and time your shots with the DMR 
watch for the "yellow spakrs" indicating the enemy shield is down. 
 
keep playing pretty much

Good stuff, thanks for the tips and links guys!

• Aim for the head 
• Crouch
• Hit dudes when their shields are down

" Camp some more, it's basically the only effective in Halo. Thanks to the regenerating health system, the worst thing to happen to the gaming industry ever. "

Try some Firefight!
Either make a custom game for yourself vs some elites (Heroic or harder) and practice taking them out with standard weapons like the DMR/AR or try Score Attack/Sniperfight in the online solo firefight.
I play a good bit of score attack each day and when fighting skirmishers, jackals or elites you can really practice on reflex shots or taking something out from afar.
 
Other then that, play, play, play and play some more!