Remember that the tricep is 2/3 the arm mass/size. I don't normally train arms by themselves as they are borderline too big for a balanced physique. But if you feel like yours are lagging behind, then by all means give them their own training day.
I would superset biceps and triceps together. Vary the angles and rep schemes to hit different heads and exhaust the small and large twitch muscle fibers.
I like using the preacher bench and alternate sets going narrow then wide. If you like dumbells, concentrate on minimum elbow swing, taking the shoulder out of the movement.
Another good one I've recently seen and added is a facedown approach on a incline bench. The start of the move is fairly easy but the top is much tougher.
For triceps, I like rope pushdowns with an arm twist at the bottom, and an overhead move for the long head of the tricep. You can use a heavy dumbell or rope pulley or both. Lately Ive also added bent over pulley kickbacks with single arm focusing on the squeeze, it really works the side of the horseshoe