Finding the Right Fit
There are dozens, possibly hundreds, of "Minecraft" resource packs available -- see the Resources section for a selection of links. Whether you're looking for a high resolution, realistic look for your game or you want to completely change things over to a science fiction theme, there are options. Find the one that fits your needs and don't be afraid to experiment with different options. You can easily choose between installed packs from inside the game without causing problems in your saved worlds.
Installing the New Resources
Locate your downloaded resource pack and move it to the "Minecraft" appdata folder. On a Windows PC this will be at "%appdata%\.minecraft\resourcepacks\". It should be in a ZIP archive by default. There is nothing more to the installation process as the game will detect all pack archives in this location.
Making Your Selection
Launch your game and log in. From the main menu you can open the options screen. This will present you with a Resource Packs button. Once you click that button all available resource packs will be laid out along with a preview of the new appearance they will apply to your worlds.
Watching Your Framerate
The more detail that your new resource pack adds to your game, the more it reduces your computer's performance. Packs with extremely high resolution can bring even fairly powerful computers to a standstill. If you notice skipping or slow refresh rates then it might be time to find an option that's less resource intensive.