If your computer spec lurks somewhere near or below the edge of the recommended minimum system requirements you have probably noticed that the option to disable shadows is not offered in the launcher, and consequently may have noticed that the low quality shadow settings look like garbage. These mods will increase performance, depending on a computer's specs, but will degrade graphics:

If less things are being draw on-screen at the same time, it means your hardware is using less processing power to achieve the same thing, and it automatically converts in better performance. What these occlusion planes do is unrender parts of the cell/objects/NPCs that are not being seen by the player, in most cases behind a wall or above/below floors (occluded). a feature called Occlusion Culling, where manually puts occlusion planes in some spots of the interiors to improve performance. INI setting to also use injectSMAA with ENBSeries) InjectSMAA - like FXAA, but looks and performs better (disable FXAA if using this if using ENBSeries, use the 'ProxyLibrary'. Skyrim Performance PLUS - installing it will give little (unnoticeable) graphics degradation, while certain CPU-intensive effects (falling rain, snow, leaves, etc.) are underway Unofficial Skyrim Patch - a comprehensive bugfixing mod also contains a 'savegame debloatifier' feature that may help improve performance THIS WILL NOT DEGRADE QUALITY IN ANY WAY TO INCREASE PERFORMANCE. THIS IS NOT A GRAPHIC MODIFICATION, so feel free to use with vanilla game. Have you tired from CTDs when your game is heavily modded? Unable to install HD texture packs without CTDs or travel in the world very fast? This patch fixes the problem and also brings you higher performance even without memory fixes enabled. Some mods or software that you could use to increase performance:

How to improve skyrim fps