Well, that's a deep question.
(smile) Well, and deep is a play on the words and topic. Let's not fall into that well.
OK, to disable items to start up I first see if the app has it in their menus. Skype for example. After that we can look in the usual Startup group and delete items or move them to a fun named NOSTART group.
And we always love to read Black Viper's site on the OS in question (google BLACK VIPERS WINDOWS to find that.)
In closing, the best tool I have is google and an app called HIJACKTHIS. That's a power tool and I use it at first to learn all about my PC along with Google on each item in the report. I strongly suggest you never use this at first for just the report. As you get more knowledgeable you will find this tool very sharp and able to knock off a specific item that you can't seem to eject any other way.