You definitely want to use a mod manager utility of some sort. They make installing easier and, perhaps more importantly, make uninstalling easier.
Oblvion Mod Manager (OBMM) is such a utility. It has been around for a long time and does a nice job. But you have other options.
Bash Installer (BAIN) is the installation utility that comes with Wrye Bash. It can do quite a bit more than OBMM but has a steeper learning curve.
Although I know nothing about it, my understanding is that you can also use Nexus Mod Manager (NMM) as a mod manager utility.
I use Wrye Bash for some of its utility support (like easily repairing the A-Bomb), but I use OBMM instead of BAIN for managing mods. That is simply because I started with OBMM and am comfortable with it. Most avid mod users that I know that have taken the time to learn BAIN prefer it as the top choice of mod managers for Oblivion. If just starting out, I would absolutely focus on looking into BAIN.
Before you start, you want to find out from Steam users if there are any unique aspects of a steam installation that affect modding.
Assuming it is the same as a disc install, you want to install Oblivion in a place other than its default choice of 'Program Files'. This is because Windows gives programs installed there additional 'virus protection' type treatment that can interfere with installing mods.
Happily, Renee Gade IV is also learning the ins and outs of modding Oblivion and there is some good discussion of the process in her thread (RG4's PC Modding Crisis Thread) in this same sub forum. I recommend you review the sage advice therein. As you will see, there are several folks here who are much smarter when it comes to modding Oblivion than I.
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