Before you go anywhere you need to define some basic parameters.
For example, what do you want/intend to 'clean up'?
It sounds like a dumb question, but it isn't.
No script can decide for you what your 'cleaning' should consist of - sure, it can find old files, or big files, or files with specific names, or in specific directories, or owned by specific users, or any number of other parameters, but you're the one that has to define the scope and the limit... HOW old? How big? What names?, etc.
Once you know what your rules are you can look at different implementation options, but as it stands there really isn't much you can do since your target is ill-defined.
Then you need to make sure your data is backed up properly. At some point, one day, ANY 'clean-up' task, whether manual or automated) is going to throw away a file that someone absolutely desperately needs. It's going to happen, and you will need a backup of your data that you can fall back to.
As a final thought, computers perform this task pretty awfully - there's often too much subjectivity in deciding what is worth keeping. Don't be surprised if your cleaning 'process' comes down to you dedicating an hour or two every week/month to take a look at what's there, rather than a headless automated script.