If you're just playing single player (not using internet) then it could be simply that you've not dedicated enough RAM to your Minecraft. Simply open a .txt file, write in
then save as a .BAT file (Minecraft.bat) and run it. You should find reduced lag.
You could also get Optifine as a mod (reduces lag by giving more options) or just put down your settings.
One last thing: Is everything updated - Java, Minecraft, and is your OS 64BIT?
HELPpls halp
javaw -Xmx2048m -Xms2048m "C:<your minecraft directory>\Minecraft.exe"
then save as a .BAT file (Minecraft.bat) and run it. You should find reduced lag.
You could also get Optifine as a mod (reduces lag by giving more options) or just put down your settings.
One last thing: Is everything updated - Java, Minecraft, and is your OS 64BIT?