First things first, Get rid of the lifting straps. I don't use them at all--except on heavy lifts such as deadlifts and shrugs (some need them). By not using them my forearm development has doubled. It not only increases size but it also increases forearm strength. Basically, when lifting straps are used the forearm muscles are barely used at all. Try this for about 6-8 weeks and I promise you will see the difference.
My basic forearm routine is this:
I stay with this routine every week but I will change the order, sets, reps and weight used almost weekly.
My usual routine consists of the same exercises but I do 4 sets of 20-25 reps for every set and every exercise. This routine really makes you feel like ripping your forearms off because they burn so BAD. This one is my favorite.
Forearms are about like calves, in that you really need to use good form and concentrate on the muscle being trained. On wrist curls always make sure you go all the way up and all the way down. Also, on hammer curls, concentrate on the muscle being trained, if not you will be working too much bicep. Hold every rep and contract the muscle and you will definitely feel the burn.
I train my forearms only once a week, although sometimes I will do them twice a week, my best results come from only once a week. Your forearms come into play a lot when training back so I avoid training them near my back day. I train my back on Friday so I will do my forearms on Wednesday. Just keep track of what works best for you.
Now, make your forearms look like Popeye's.