Before installing the mods, a couple of other files has to be installed
1 - If you haven't already, sign up at the Nexus. (LINK)
It's free, and it takes 2 minutes. The Nexus is a great site for mods in general, so it's definitely worth the time.
2 - Download and install the NexusModManager, "NMM". (LINK) *Install descriptions are found at the Nexus page if needed.
Download and install
"Skyrim Script Extender".
If you have the Steam version, download from the Steam workshop instead: (LINK)
If you have the another digital version or the DVD version, then download from the SKSE website: (LINK)
*You can either download SKSE in a .7z package or as an installer. If you choose the package, just unpack the files into the root of the Skyrim game folder. Now make a shortcut to "skse_loader.exe", and use this shortcut to launch Skyrim from now on.
4 - Download and install TES5Edit. (LINK)
Unpack and copy the files to any directory, then make a shortcut to "TES5Edit.exe".
This tool is used to clean up Bethesda's "lazy edits" from their DLCs. See description in the Cleaning section. (LINK)
5 - Download "TES 5 ESS Files Editor". (LINK)
Download the latest version and unpack the files to any directory. Make a shortcut to "TESVESSE.exe".
*If you plan to start a new game after SBP installation, this file is not absolutely necessary, but I still recommend it. If you want to continue a saved game, you definitely need this tool. It's used to remove old script data from a save-game file. Unfortunately Skyrim stores scripts in the save-game files, so if you remove a mod which contains scripts, then the scripts stay in the save-game, and can cause all kinds of errors.
6 - Find out how much video memory you have on your graphics card.
If you are not sure, use this tool made by Boris Vorontsov. (LINK)
7 - Make some coffee and get ready for several hours of downloading and installing. It's a long time, but remember at the end you will get the result of several months work.
Curious if the results are worth the effort? Here are a few before/after screenshots to give you an idea
Before/After Screenshots (SBP 3.14)
Before/After Screenshots (SBP 2.54)