I would first delete any obvious temporary files (like ones begining with ~ or ending with .tmp or where the size is 0 bytes, etc.). Then I would zip all the remaining files to another location. After that I would delete everything else. That way ifsome of the files were important or needed files, you have them backed-up and can get them restored. You, or an application, may be mistakenly saving user docs or files to the Temp dir. If everything works fine after a given amount of time, then youcan delete the back-up files.
Then, I would inspect the default settings for the folders where your user files are getting save to for the applications that may come in question - usually in the application under Extras/Options, or something like that - and see if any are set to the Temp dir by mistake.
Once you are sure that your files are not getting saved to the Temp folder, then usually you can regularly delete everything in it (some files cannot be deleted right away - like locked files that are currently in use by the system or an application - these usually have todays date).