Source: http://lifehacker.com/how-to-clean-out-your-overflowing-hard-drive-and-get-yo-510511720
Hard drives get messy. You save files and forget them, download huge chunks of data that pile up, and change your naming schemes a hundred times. It's spring, though, so why not do a little tidying up?
To make things simpler, we're going to look at this from the perspective of cleaning up a secondary drive that doesn't have an OS installed on it. You can use these same tactics for any drive, but there are other ways to save space on a system drive including clearing caches, eliminating old temp folders, etc. Right now, though, we just want to focus on your junk.
Find the Really Big Files
When you need to clear up hard drive space in a hurry, the first thing you want to do is find out just what's taking up all that space. WinDirStat is a crowd favorite
Get Rid of Duplicate Files
Whether they're big or small, duplicate files take up unnecessary space. Windows, Mac, and Linux users can all use the handy Duplicate File Searcher
Find the Really Old Files
Finding the big stuff isn't always helpful. After all, you probably downloaded those giant videos for a reason. If you'd rather just find the old stuff, you can do that with simple search operators in the search box for Windows 7 and up. You can search for the last date modified, accessed, or when a file was created, and further sub-filter by size or type. Unfortunately this method lacks the nice visualization of file size that WinDirStat has, but it can go a long way in whittling down the stuff you don't need or use anymore. There are bunch more search operators you can use to narrow down your searches here.
Rename Your Files
Okay, so you definitely want to keep those 12,462 wedding photos, but wouldn't it be nice if they were named something better than IMG01827.jpg? Batch rename apps allow you to bring a more uniform sorting scheme to your collections. Apps like Rapid Streams
Move Your Files
Now that all your files have meaningful names, put them somewhere equally meaningful. Apps like TeraCopy
Keep Your Private Files Really Hidden
Most of us have something that we'd rather not share with the world. Sensitive work documents, birthday gift ideas, etc. You can hide files in both Windows and OS X
If you're like me, you probably have years and years worth of files laying around on your system that need to be cleared out, but it's not necessary to go through them by hand to clean them up.