Solo-Wing said:
One of the first things you should be downloading. It's Oblivion Script Extender. Some mods, especially the larger ones, will not run without it.
You then want Oblivion Mod Manager. You will find that on the TESNexus.
You will also need to hunt down ArchiveInvalidation Invalidated. I'll save you the trouble.
http://www.tesnexus.com/downloads/file.php?id=10724
Quite a few mods need that to run. You can toggle Archive Invalidation in Mod Manager but it's recommended you download that mod, it's just easier.
You will then need BOSS, Better Oblivion Sorting Software. That will correct your load order for the mods and make sure there are no conflicts that would cause issues, say for example you have 2 mods that both occupy the same world space it will warn you and you'll then delete one. Load order is important because if you have a mod that requires a master to run and it's loaded before the master then you'll probably have crashes. Use BOSS and all your problems will be solved.
So many times i've seen people on forums complaining a mod they downloaded "broke their game" because they don't use any of the tools. Mods will very rarely have any issues, the main problem is people trying to play around with mods without using any of the tools to help them.
And finally.
When you get a bit bored of Oblivion in it's original state then try this mod....
http://www.nehrim.de/indexEV.html
It's a complete overhaul of Oblivion and pretty much makes it an entirely new game.