How to Install Optifine for Minecraft 1.8.
Optifine have released a stand alone jar file that lets you play Minecraft 1.8 with all the benefits of Optifine. It is still in test stages so some features are missing but they are being added and worked on.
Visit the link below and download the 1.8 version
Click on the installer you just downloaded. This should automatically install the new Optifine for Minecraft 1.8. It will also create a profile in your Minecraft launcher called "Optifine".
Open up your MC launcher and select the Optifine profile. Once selected your should see somethin like "Minecraft Optifine 1.8" in the bottom right hand corner.
Click "Play" and enjoy.