One of my first installed is Firefox with either Advanced System Care or Wise Care 360 next. While I use MS' built in AV app, I also install Ashampoo's AV early in the piece as well. Then I install my Stardock apps along with Winstep Xtreme. After that I install my video and music apps for editing and converting, etc.
After that it's whatever I find useful, like RightClick Enhancer..... while not forgetting various drivers as required. For graphics card drivers I prefer the proper Nvidia or AMD drivers to the generic ones MS put out.... same with my Soundcard drivers and associated software, I prefer the Creative Labs releases.