If you speak japanese and you're good looking, it would be very easy to star in a JAV...but it's maybe not as fun as you could imagine..
YOu can find ads every months on producers' blog or directly on the companies HP. I recommand you to contact SOD production, they have a good reputation in the industry.
You need to have a proper visa, working/spouse visa, so no student visa or tourist visa.
Just need to send an email with pictures, name, address, phone number and what you would like to do (bukkake, SM,eScato, etc..) but you'll never have a scene with a girl from the start. You'll begin your "career" with bukakke, SM, Dildo , etc..
Most of the time you'll basically wait in an hallway masturbating yourself with 30/50 other dudes around waiting to give their loads :dies:...Honestly that's not my thing.
IF you become a regular, you could have a blowjob scene but to get a full scene, you'll have to wait months...
You'll get paid from 3000yens to 10.000yens depending on the scene. MAximum 40.000yens if you become "famous" in the industry.
I've met few foreigners, in their 30ths, forced to take Viagra as they couldn't get hard stressed by all the dudes around.
Personally, i prefer hanging around Roppongi and grap a nice girl for the night than having 50 japanese dude masturbating around me.. but that's up to you