About Mods:
The #1 thing you need to know:
Really good and trusted modder's mods WILL CONFLICT with other really good and trusted modders's mods. I cannot emphasize this enough. MOD CONFLICTS HAPPEN! It is the nature of the way this game is modded.
Therefore, resolving conflicts is up to the person playing the game. That is you, and no one else can fix it for you. It is entirely YOUR responsibility. (I will talk about the "how-tos" of resolving mod conflicts in detail, later.)
The #2 thing you need to know:
A really good and trusted modder is NOT MORALLY REQUIRED to make sure their mods work well with another really good and trusted modder's mods. DO NOT ask one modder to "fix" their mod because it conflicts with another modder's mods. When you experience a conflict, you must choose between mods. Period. (So, when you see that a modder HAS put out a version of their mod that resolves a conflict, APPRECIATE that modder and thank them with all your heart -- they went way above and beyond the call of duty, and they are a star in the firmament.)
The #3 thing you need to know:
Not all mods are created the same way. A modder who is able to make amazing override mods is not expected to have mastered scripting mods or XML mods. People who have mastered all those are still not expected to know how to make core mods. Object mods are not the same as mods that change the game, itself. Mods that require changes in animations are more difficult than mods that do not need additional animations. In short, you CANNOT expect a really good and trusted modder to do something that they are not qualified to do, which is why many, many modders will not take requests. (I will be talking about the different types of mods in more detail, later.)
The #4 thing you need to know:
No two people play the game the same way. Asking others for their favorite mods, while very interesting and enlightening, IS NOT the way to choose mods for your own personal game. They don't play the way you play, so their experiences will only let you know more about the way they play their game. The ONLY real way to choose mods for your own game is to get out their and look at mods, to see for yourself. That being said, certain websites have mods generally used by people modding their game. Which particular modders on those websites you can personally trust with your game, the way you play, will be a matter of trial and error. Because only YOU play the way you do.
The #5 thing you need to know:
Mods need testing. (EDIT: Only test mods that are made for your patch level. Safe 1.63 mods MAY NOT WORK with patch level 1.67, so you must get updated mods and/or match your patch level with your mod level.) YOU must test mods. Did I mention that in your game, the way you play, every single mod you ever use will need to be individually tested? Did I emphasize enough that YOU have to test whatever mods you use? Individually testing a mod means you play in a test game with that mod, and ONLY that mod, for at least a sim week, to kick up any problems, and to figure out how the mod actually works, what it actually does, and whether or not that mod is a good fit for you. This will take time. It will be worth your while. Testing individual mods IS NOT optional. YOU HAVE BEEN WARNED.
The #6 thing you need to know:
Core mods are dangerous. They change your game, at a deep level. They may affect the game in ways you cannot easily fix, if you need to ever remove the mod. Core mods that make the claim to not permanently change things and claim to be removable still DO change things at a level too deep for you to see the changes.
In my personal opinion, and from my personal experience, I advise you to plan on keeping a core mod in your game for whatever save you EVER used that core mod in. Truly. I know people will tell you they have gotten by with removing core mods. But ... that has NOT been my experience. I'll leave it at that. YMMV.
Choosing a core mod IS THE MOST IMPORTANT mod choice you will make, because core mods do not play well with each other. Generally speaking, you should choose ONLY ONE core modder, and then find other non-core mods to flesh out the changes you wish to make to your game, always ensuring that all other mods do not adversely affect the core mod.
Core mods are the most useful mods and give you the most control over how you play your game. You will likely want to use a core mod. Which means you will live dangerously, until the mod is thoroughly tested.
Core mods need to be tested for at least three sim weeks, because they do so much, and have the highest learning curve. You will not be able to make an informed choice about their safety and usage in your game if you do not take an adequate amount of time to test the mod. Test with a factory reset test game. DO NOT test a core mod with your real save.
Once a core mod is thoroughly tested in a test game, then test it with a COPY of your real save, for the same extended period of time. If you do not adequately test your core mod, you may be making a big mistake. You have been warned.
The #7 thing you need to know:
You will need to make some hard choices. Once you have individually tested all non-core mods, the next step is to individually test your chosen non-core mods along with your chosen core mod. Yes, that is twice the work. Yes, it is necessary to test twice. No, you cannot skip a step and simply test all your non-core mods with your chosen core mod.
Why? Because you need to make informed choices. You need to know, when it comes down to eliminating conflicts, which mods are REALLY the most important to you, and which you can and will (possibly regretfully) live without. Because, in this game, you CANNOT have it all.
I'm going to post this much, right now. I'll go into more detail, but it will take me some time to write it up, so stay tuned. (I'll also add this to my Know Your Game thread.)