T3 with external flash - What settings?

Pretty new to the flash world. I am using a Nissin Di622 II on a T3 for portraits and such. Here are some settings I've been using.
Av Mode
Auto ISO
Evaluative metering

Any recommended setting on the camera or flash? Also, how does back button focusing with the shutter button half-press being the AE lock effect the flash?

auto ISO is tricky with flash.
Since this flash is ETTL, I would set the camera on manual, shutter to the synch speed, set the iso to anything you want (start at 200, or 400),aperture at f5.6 and just shoot. Of course, you will run into the limitations of ettl in some situations.

The easiest way to learn ettl flash is manual mode. Av with auto-ISO will get you nothing but ISO 400. As a general rule, I set my ISO to 100 x the reciprocal of the aperture. f/4 = ISO 400, f/2.8 = ISO 320, f/11 = ISO 1250, and so on. Use the shutter speed to control ambient.

Blake,,,,,with flash you'll get the best results if you choose totally manual on your camera. Select to camera's shutter speed, aperture and ISO yourself.

As a starting point, put the flash in TTL. Camera at 1/125th second at 200 ISO, the lens on f/5.6 or f/8. Play around with different camera to subject distances, apertures, shutter speeds and ISO until you get the results you desire.

No one setting fits all.

Read this small article
http://www.learn.usa.c​anon.com …_highspeedsync_​blog.shtml

I like using H>> on flash whenever I'm outside and just want fill flash.
If I'm inside, Manual mode on camera serves me best.