Some mods are no longer relevant and have been replaced by more modern and stable mods, although you may still see many references to these older mods. It should be noted that this is not intended to bash authors in any way.
Wet and Cold is replaced by R.A.S.S. and Wet and Cold - Gear
Amazing Follower Tweaks (AFT) or any other follower framework is replaced by Nether's Follower Framework (NFF)
Immersive Citizens - AI Overhaul is replaced by AI Overhaul
Achievements Mods Enabler is no longer needed as SSE Engine Fixes includes this fix
Flora Respawn Fix is replaced by Wiseman303's Flora Fixes or Scrambled Bugs
Ecotone Dual Sheath or All Geared Up Derivative (AllGUD) are replaced by Simple Dual Sheath and Immersive Equipment Displays
The Paarthurnax Dilemma is replaced by Paarthurnax - Quest Expansion
HDT-SMP is replaced by FSMP - Faster HDT-SMP
FNIS is replaced by Nemesis. (more on this here). which is replaced further by Pandora. Use Pandora rather than the first two.
Immersive Armors and Weapons are huge and convenient armor and weapon packs, but their leveled list integration is messy, they're very buggy and their contents vary wildly in quality. Although there isn’t anything quite to their scale, there are tons of newer and better gear compilations on Nexus and other sites to find. Some packs we recommend are Armor Variants Expansion, Warmonger Armory, Reforging - To the Masses, Animated Armoury and Heavy Armory. A Reddit user compiled lists of armor and weapon packs (as well as other lists, be sure to check their profile). If you really must use Immersive Armors, you can use the Immersive Armors Retexture and Mesh Fixes.
Complete Alchemy and Cooking Overhaul is notoriously incompatible with… nearly everything, and its users often find their load-order loaded with patches for it. It also suffers from feature creep, frequently touching things outside its scope. Gourmet - A Cooking Overhaul and Apothecary - An Alchemy Overhaul are alternatives, but they too, require quite a few patches.
Weapons Armor Clothing and Clutter Fixes (WACCF) also suffers from major feature creep and is an overall patching nightmare. This user went on a long rant about it. Weapon Armor Attribute Tweaks is a "simpler" approach, still use with caution.
Open Cities, while a cool idea, is simply a proof of concept. It requires a patch for every single mod that edits cities in any way, including mods that add new NPCs or AI. SR Exterior Cities may be a modern alternative, as it contains a synthesis patcher to generate patches.