Heavy rows FIRST for biceps, heavy pressing for triceps. If you have a strong bench and a strong row, or even deadlift, you'll have strong bi's and tri's that can handle heavier loads when you isolate them.
For the long head of the triceps, I love overhead movements with a good stretch at the bottom. Keep the weight heavy but don't sacrifice form.
Biceps seem to grow for me with a heavy barbell curl or ez bar. Again, keep weight heavy but with good form.
You may need to increase frequency and overall volume. Try to prioritize them if they're truly lagging. I like the suggestion of giving them their own day and seeing what happens.