Hi, my friend on a server was having a hard time installing optifine so i am making this for him.
step 1: get a clean Jar file - I do not know if force update gets you a new jar but what i do is take all of the important items in the .minecraft folder (Saves, texture packs, servers, pics, etc.) and back them up in a seperate folder. next I delete everything else in the .minecraft folder (But DONT delete the minecraft folder itself). Finally, open up minecraft and you will have a brand new minecraft.
step 2 : download optifine/a zip archive program (i use 7zip)
step 3: open up the minecraft.jar file in the /bin folder and delete the meta-inf folder.
step 4: copy all contents inside the optifine zip file to the jar file and open up minecraft again.
if you have correctly installed optifine go into the video options and you will see more options in it. also remember to put the stuff u backed up back into the .minecraft folder.