1) Perform the most effective exercises first
When training your arms, perform the most-effective exercises early in the workout. What are the most effective ones? Those that recruit the maximum amount of muscle fibres. For example, the triceps has three heads: long head, lateral head and medial head. So perform a move that works all three at once, rather than just one or two. A practical way to determine which exercises activate the most muscle fibres is by how much weight can be used in those exercises, obviously assuming proper form is respected. This means dips on V-bars will do far more for your triceps development that kick-backs or pull-downs.
2) Favour seated arm exercises over standing
Seated isolation exercises are essential in achieving maximum arm hypertrophy. When you’re seated you don’t waste any effort stabilising the body, so you can focus more effort on the lift you're performing.
3) Use thick-handled dumb-bells and barbells
I have been a huge fan of thick-handled weights since 1982, for these reasons: they increase motor unit activation; build functional strength; provide a great grip and forearm workout; and correct any imbalances between your dominant and no-dominant arms.
These tips came from Poliquin's book Bigger, Stronger Arms. You can buy it from his online store. For more workout advice from the legendary strength coach, pick up the January 2011 issue of Men's Fitness.