The iPhone 16GB entry level model's problem with most of us is that the storage is not enough in any measure. Most of the entry level models of Android flagship smartphones ships with 32GB or they have an option for expanding. Apple may or may not kill the 16 GB model as reported in this CNET article, but for those who are stuck with the 16 GB model, here are some tips that helps you to reduce the storage space.
iPhone 16GB's "storage almost full" troubleshoot
Bug bug bug
While some apple fans may deride me when I put bug as a reason but indeed it is true. Find out in iTunes whether you really have consumed that amount of data. Do a backup and restore helps in most of the occasions.
Update to the latest OS
If you are thinking a latest OS comes with heavy features and occupies more space, then you are onlt half right. Apple is making all efforts to make its iOS updates as much lean as possible.
The cache problem
The iOS never gives you an option to clear cache of applications. Some apps like Twitter, Facebook or others occupy huge amount of space because of the bug in cache clearing. I particularly had problem with Twitter app, which used to occupy more than 1GB space at times.
Finding out the cache size
Under Storage, Manage Storage
In case you find out any of your social media apps occupying a disproportionate space then the problem is with the cache of these file.
Since iOS does not let you remove the cache manually, the only option left with you is to delete and reinstall the app.