I'm no expert, but guard passing is probably the best part of my game. I don't really try to do any particular pass and I don't think of passes as certain techniques, like an armbar from guard or somethign. I try to keep certain postures and apply cetain pressures depending on what my opponent is doing. One thing I always try to fight for, wether in a combat base, or standing is inside position. Grips on the inside of the legs, grabing the pant if gi, and I try to grab at the top of the shin near the knees no gi. If I can control his inside, I think I have a decent chance of passing. I try and keep my posture good-head up, elbows tight to body.
Once I have my grips, it depends on what he is doing. If he is pushing hard against my grips maybe I'll slide my hands under and pass like that. If he is pushing real hard I'll try to zone his legs out and go around. Most of the time I'll try to put his legs one side of center or another as he fights the grips, I'll try to sprawl on his legs and smash his hips and then pass around to his back side. Mostly though its about getting that inside control you control the legs, control the hips and all kinds of passes open up.
Half guard I use more structured passes, but first thing I try to do is kill their posture. Flatten them open with my head, or a cross face and fight for that far side under hook. If I win that battle I think odds are with me passing, so that is the battle I'm putting all my effort into.