You're pretty much using them to their highest potential with the loadout that you mentioned. Tactics wise use them to beat on things that your Tactical Squads would struggle with, but don't go after true assault specialists. Assault squads are fine at beating on say Necron Warriors but won't have much luck against units like Howling Banshees. Mostly with Codex Marines though, Assault Squads are at their best when used as a counter-attacking unit. Instead of going and looking for fights, use them to hang back and intercept units that are attempting to cause you trouble.