I have gone very long periods not training forearms directly but that has changed now. I love training them and it definitely makes a huge difference. I like using barbells, cables and db's. I usually do hammer curls, wrist curls and reverse curls.
I do hammer curls standing, sitting or on a preacher bench. I rotate between db's or cables.
Wrist curls I do supinated and pronated with db's, barbells or cables. I love doing the behind the back wrist curls seen in the video.
My fav are probably pronated wrist curls using a cale machine. I move back about 4 feet from the machine and the pump is incredible.
Any back movement you use heavy weights is also great and I used to do farmers walks when I had the space and heavier db's.