Skyrim Total Enhancement Project (STEP)
STEP is a comprehensive guide to installing the best mods, tweaks and settings to enhance your gaming experience in Skyrim. STEP tries to stay as close to the vanilla Skyrim as possible while improving graphics and fixing game-play mechanics, so nothing lore-breaking or outrageous. Currently, STEP lists over 200 mods and you can install all of them if your PC can handle it or you can pick and choose which ones you want.
STEP is massive and even though the wiki provide detailed instructions, it can be a bit intimidating to a beginner. This article by Joshua Derocher explains STEP in more layman terms; think of it as a guide to the STEP guide. At the end of the article, Derocher also recommends two additional mods to install along with STEP. Do note that the links in the article are linking back to an older version of STEP. Be sure to always go to the STEP main page to get the latest guide.
I am currently using around 80 mods from STEP. Going the STEP route takes some commitment as you will take many hours to set up your PC, read up and install mods and utilities. While it is possible to port over an existing character, I decided start from scratch (as recommended by STEP) to prevent errors in the game. I’m happy with how much STEP improves the game and looks. My screenshots are still not as good as the master but I am satisfied with the results on my 3 yo PC.
See my list of installed mods
ENBSeries is a powerful post processing modification tool available for Skyrim and other games. It was developed by Boris Vorontsov; who still maintains and updates the product. This tool enables users to create custom configurations (ENBs) designed to their own specifications by modifying rendering functions and the application of additional effects such as bloom, depth of field, and SSAO. ENBs often enhance overall lighting, colors, and shadows among other aspects of the game, but comes with a performance loss of anywhere between 5% to 50% of your total frames per second (FPS); depending on your hardware setup and the ENB features you use. Most find this loss acceptable compared to the enhancements and features gained from the ENB.
Taken from STEP Project Wiki
(because they explained it better than me)
I used to use ENBs but they slowed my game so much that I had to turn it off during gaming and turned it on only when I take screenshots. They are not perfect and none works in all situations but they are pretty amazing when they work well. Click here to see examples of ENB.
Update 18 October 2015: I am now using Phinix Natural ENB. Below are some comparison screenshots. Click on the thumbnails below to view the larger image.