An often overlooked way to save space on a budget device is to use your browser to access social media sites instead of using the apps for those sites.
Facebook, for example, can grow to be quite large.
On your browser, it could be mearly another bookmark.
The browser is already there, why not use it?
Instagram, Pinterest, Tumblr, and whatever else social media site you can think of are all easilly accessed with a browser that takes up a fraction of the space.
Youtube is another one.
All of the individual apps can be uninstalled, and just use your browser- have a bookmark for each site that you wish.
Also, any videos and pictures that you have on the device, along with music and documents should be stored onto the SD card.
Basically, the card is there for you to store personal media on, and the device memory is there for apps that read this media and also allow for internet access.