EDIT: To reset (vanilla) your ME3 installation, see here: http://ottemis.tumblr.com/post/57665984 ... lorer-info
This is important if your mod installation breaks or you are having problems, first vanilla everything and make sure it wasn't your fault.
I thought I'd make this tutorial since the method has changed since the last tutorial.
Basically, I'll go through how to install mods from tpf, but this applies to simply installing mods too I guess.
I'll start from a tpf.
So, start ME3Explorer and through there, Texplorer.
If this is the first time you've run Texplorer, it'll ask if you want to edit DLC contents. It's up to you, but if you don't, the DLC's will have none of the mod improvements.
NOTE: This will at least double the scan time, and take up nearly 20GB on your hard drive (but it's totally worth it).
Once that's done, there will be a lovely tree with tonnes of folders with things in them that you don't need to worry about anymore. Find and start "Mod generation". NOTE THE RESIZE!
Select the .tpf you want to make into a .mod, and this will come up. Note the star on the bottom two. That means something is different between the files in the .tpf and the files it's going to replace. The blue arrow shows one that is fine. I'll go through how to fix it at the end seeing as most people won't need to. If you have *'s, keep the window open and go to the bottom of this tute.
If you get errors about not being able to find textures in texplorer, it may be due to you not having some DLC that the tpf creator had.
Once it's decided it likes all the textures, go ahead and generate the .mod.
Save it somewhere and close texplorer. Then open ModMaker from the menus.
Load the mod/s you want to install. Note here that the more mods you load, the longer it will take and the more likely that the program will crash. It can now handle quite a bit, but consider yourself warned.
Now you can run all or some. Not sure why you'd only want to run some, but the option is there.
Now wait till they finish! I recommend not doing much with your computer while this happens. It reduces the possibility of crashes and stops you from getting annoyed at the lag it produces.
----- HOW TO FIX FORMATTING/MIPMAPS -----
First you have to extract the textures from the .dds. Do this either with tpfextract (google), or Salt's version which is on the forums here.
Then you need to know which one is broken, so that mod screen with the asterisks tells you which texture is wrong. Go find it with the search tools in Texplorer and right click -> properties, and look at the format part. It'll be DXT1, DXT5, or V8U8. If it's others, they aren't really supported yet. Preview it too so you know what it looks like, so you can find it in the .tpf extracted stuff.
I know Photoshop and gimp have .dds plugins and they work most of the time, but they really hates normal maps, plus Photoshop isn't free. So the easiest way is to get the (free) Directx SDK from Microsoft. Get the June 2010 version (I think) as it contains the tools necessary.
To get started, open the Texture Tool. Don't worry about the 64 bit thing there, just open one. Then open the .dds in question with it.
Now, to fix it, you have to know what's wrong. Common problems are no mipmaps, in which case you use the "Generate mipmaps" function, and save. The other is incorrect formatting. Find the same texture you looked at in Texplorer, and change its surface format, save and exit.
In the Mod Generation window (which you kept open), click Matching and choose the file you just fixed.
Then proceed as normal (above)
If you have problems, SEARCH THE FORUMS FIRST!! There are lots of tutes, and if you have a bug, look through the appropriate bug report before asking the same question that's been answered 10 times in that same thread. If you can't find it, or have more information, then let us know.