tease the key you work in with pads & strings, chords, whatever fits the bill. theres always the option of taking any sound you made and putting a completely wet reverb on it record it out, reverse it, timestretch it, granulize it, you get the idea. intro for me usually is some pads, reverbs, delays, eerie kinda stuff. in the buildup you can start moving torwards the actual theme of the tune by teasing some of the basses with a highpass filter (to not give away everything right away) and maybe a filtered build up drumloop of the original break leading into the actual drop. just look at intros of artists whose tunes you admire or that are in the vein of the style you're going for, that usually is inspiring enough to come up with your own ideas.