A Minecraft FPS Boost Client ?

Installing OptiFine will help a lot. It tends to give a ton of extra FPS, especially if you follow a YouTube tutorial or something similar that shows you how to set it up and optimize it properly.
If you're new to Minecraft and can't use OptiFine, or just haven't had a look... Open up the settings and mess around with some of the options under graphics. Disabling VSync will help you gain a ton of frames if you're locked to 60 or something similar. Just a few small changes can make a world of difference.