No, this is not like all these other bullcrap things on lag that I've found. I realized that there's really no good tutuorials to help with lag, and all the information is scattered. So, I'm putting it all in one place.

First off: OptiFine

DUH! This is the most obvious way to solve minecraft lag. It helped a little for me, but every little bit helps. Turn the settings as low as bearable for you.
http://www.optifine.net

Second: FPS++

This is another mod that helps with fram rate. Not as helpful as OptiFine, but it still works. It's also compatible with OptiFine.
http://www.minecraftdl.com/fps-mod/

Third: This only works for laptops: Battery Performance

Set it on HIGH PERFORMANCE. This really does help! Click on the batter icon, click "More Power Options" then clikc High Performance

Fourth: Java on High Priority

This apparently works for some people, but now me. Go to Task Manager, More Porcesses, right click javaw.exe, then set priority on High, NOT REALTIME.

Fifth: Don't Play in the Browser or Fullscreen

This helps quite a bit. It can save a good 30 FPS at times, and with the new chat setting, the chat won't cover up the whole screen when in the small window anymore

Sixth: Graphics Settings

Again, obviouse but, I'll mention them anyways:

Graphics: Fast
Advanced OpenGCL: Fast
Performance: MaxFPS
Render Distance: Short (Tiny if you can bear it)
Smooth Lighting: OFF
Particles: Minimal
Clouds: OFF

For OptiFine:
Animations: All OFF

I hope that this helped. ~Awesomesauce41