First, Create a Backup, always create backup of your important things and documents which you don't want that it should get deleted. So you should create backup in whatever you have for example: Dropbox, box, sky drive  for the documents and images. you can also create  backup's in your in your hard disk as well as in DVD's and CD's 

Second, Make sure that if you are installing the same Operating System then remove the previously installed operating system and then continue. If you are installing ubuntu, Linux or any other operating system and you don't want to remove your any other operating system that was previously installed then you can install it and  you can also change the drive as well.

Third, make sure you install the right drivers for your hardware to work properly. If you install any other driver software for your hardware then it will not word properly. But install what is recommended.

Fourth, when the reinstalling is done driver softwares are done then make sure while transferring the backup to your device make sure that you should scan it for viruses and then transfer it to you desktop or laptops.