When training biceps and triceps, include a very forceful squeeze at the end of each rep. Try to use this technique more in the beginning to middle of your biceps workout and the beginning of your triceps workout. The hard flex will drive blood into the muscle, further enhancing the work you'll do later in the session.
This technique works best with rep ranges of 6-8. Here's what it looks like using the incline concentration curl.
Notice the dumbbells are touching. Really try to push the dumbbells together and squeeze the heck out of them.
For triceps, all pushdown variations work extremely well with strong, forceful contractions too.