How to make my Minecraft run smoothly?

I have a good computer. But my minecraft runs laggy. My computer has 4 gb ram but still it runs laggy. I tried lowering the video settings on minecraft but then minecraft got really bad pixelated but still did not solve the issue though it was clear due to lowest settings. If anyone can come up with solutions that would be really appreciated.

To guess at probable issues you will have to explain all of your computer by brand and model of parts, and not just "good" and "4GB".
Minecraft runs well on Almost every new PC, but there are many old PCs that do not have the graphics performance. There are known issues with Windows 8 that may be fixable.
If you have a desktop/tower,
try to provide as much information as possible because I can't go to you to look.
http://www.belarc.com/...nload.html
Belarc Adviser is a system audit and shows some information.
Shut-down, unplug, open the pc to provide a little about the power supply.
Brand and model number of the PC?
CPU? Graphics Processor? Operating system?

The more you can describe, the more that can be guessed at for weaknesses that cause issues.
CPUs, GPUs, Power supplies, Operating System, Overheating and air flow, Drivers, cables have all been known to cause problems.