How can I improve the performance of Minecraft?

There are a number of mods that claim to improve FPS in Minecraft. My experience is limited to OptiFine (an updated version of Optimine from around version 1.2) on 1.8.1, but I do see a very significant improvement in my FPS. Although it's a bit non-specific, I have seen my FPS on a Mac go from completely unplayable to very smooth.

OptiFine (Minecraft Forum Link) reworks a number of rendering details to improve Minecraft performance (+20fps). Many people go crazy about it on the forum, others say that it just doesn't work so YMMV.

Last I heard, Notch was actually including some of these optimizations into Minecraft proper.

Keep in mind that any Minecraft mod that's not a skin requires you to patch the Minecraft code itself and thusly may not be compatible with other mods or your Minecraft version.

Within the options menu (Esc -> Options), set Graphics to Fast and set Render Distance to Tiny.

Close any programs you can spare to lose (ie internet browser, messenger, music).

If you're really desperate, you can open your task manager (Ctrl + Alt + Delete -> Start Task Manager) and select the "Processes" tab. Order by "Memory" and have a look at what's taking up so much processing power on your computer (Minecraft will be listed as javaw.exe). Use the End Process button to stop a selected process.

Do not end any processes that you don't know what they are. Have a look at the "Description" tab, and if you know what the process does, and you know you don't need it, then end it.

Of course you can change your render distance and the graphics quality, but for many, like it seems for you, the speed still is not high enough.

Now, I'm assuming that you do not have a great graphics card. For some graphics cards, like Intel HD, you will not have a chance of speeding it up without modifying the game. Optimine is common in that case. Link

If by chance you have an Intel Graphics Media Accelerator, there is another opportunity for you. GMABooster is a nice program which can boost your graphics speed quite a bit. Link

If graphics isn't your problem, and you have a slow processor/low RAM, you could try the following:

• Do not multitask. Only have Minecraft open, and don't run it in your browser. Close all programs that you don't need, even those that are behind the scenes.
• If you don't mind the lack of monsters at some times, turning the game on peaceful will reduce some load on your CPU, but of course, it takes away monsters, and that's boring!
• Change Minecraft's processing priority. A good tutorial to do that is here: Link

So that's all I can suggest. If all else fails, you might have to upgrade your computer. You can get plenty of cheap, new choices at Amazon.com.

(Plus, you could try all of those at once! The processing priority change works the best for me. I have Intel HD, and I can run Minecraft pretty smoothly.)