I too have lagging triceps. What I've noticed that helps is to designate a day for triceps alone, or placing triceps with traps and rear delts. I make sure that I haven't trained chest or shoulders recently as well.
Workouts that I notice the most muscle growth on are:
DB Extensions (go as heavy as possible to nail 8-10 reps per set) 4 X 10
Weighted Dips , again heavy as possible to make a working set of 8-10 reps
Close-grip decline bench press, 4 x 10 (failure on the last two sets)
High-intensity training, 1-1:30 minute rest between each sets. 3 minutes between each exercise.