Avoiding conflicts requires thinking.
* First, do not throw a boatload of mods into your game blindly. Think about what you're doing. Think about what you want to change in your game. Then do some research to find the mod that best suits your needs. Read everything you can. Search this forum. Search the Nexus. Google the name of the mod. The more you know, the better able you will be to avoid potential conflicts.
* If you want to avoid conflicts loading two mods that do the same thing is not a good idea.
* Use all the tools at your disposal. Learn to use BOSS, Bash, NMM. If you don't know what these acronyms mean then you're not ready to use more than one or two mods at the same time.
* Don't be afraid to ask questions. You're doing great by starting this thread. That's a good sign. Keep it up. It's better to ask a lot of questions in advance than ask for help with a broken game later on. With the exception of myself we are mostly mature, cheerful, helpful people in this forum.
Good luck!
The bolded bit is a good point to remember in particular. That's where you can run into some conflicts. I'm really new at using mods, but I can tell just from reading the specific effects listed in a number of mods that there's a very great chance of two mods creating synergistic (did I seriously just use a buzzword) effects with each other. A simple example would be if one of Mod A's effects was to make Stamina recover at 30% of the vanilla rate, while Mod B made sprinting and power attacks cost 2X stamina. One mod or the other might constitute a minor increase in difficulty, but perhaps the two in concert create a seriously difficult game.
I'm getting ready to use http://skyrim.nexusmods.com/mods/2700 and http://skyrim.nexusmods.com/mods/10037 in the same game, but both affect combat, so I made sure to ask the creator of ACE if he knew of any real conflicts. HIs suggestion was pretty simple:
Load Duel V5 before ACE and everything will work perfectly EXCEPT the Duel feature where you do less damage when your stamina is less than 10%
So there you go.