Cache clearing is only temporary though: they fill up again. Browsers and social media can cache a lot of data though, so as well as clearing their caches getting rid of any redundant apps might help (and by "redundant" I mean for example "do you actually need to give several hundred MB to Facebook when you could use a browser?" as well as "how many browsers do you need?").
Otherwise I've nothing to add beyond what I said earlier: remove unused apps, disable unneeded built-in apps. If you rooted the phone (i don't know how for this model) you might be able to use other mods to move more stuff to SD. But with an 8GB phone, which means less than 4GB available to the user, you will always be very limited.