1) back up your videos to computer n delete any long duration@not important videos..videos taken from iphone 4 is HD
2) there's tremendously big amount of songs u have there..may be a good thing to delete the songs that u never really like.
3) your active apps should be the one that u use frequently n important to you..u should backup your apps in itunes,n delete the non-important apps,especially high capacity ones..this is not pc,no??if u want the apps u deleted again,just sync to your iphone..itunes will not charge u again(in case of paid apps)

p.s. forgot to tell u..u should always have the habit to remove all apps in multitasking bar..that should help A BIT on the laggyness coz each apps will use some memory in order to run in the background(n some use data usage as well)