No clue about hearing loss for SNA. I'd imagine you need to be pretty spot on though. The test is dumb too, you sit in a room with 5 other people clicking their buttons at the same time, it makes it very difficult to tell if you just heard your own noise or someone else just clicking. My advice would be to see if you can sneak in the room when there are only a couple others waiting rather than a full line of people.
Check out the yahoo questions tips that come up when you google the MEPS depth perception test. They have a lot of tips to pass ie, don't rush even if the prompter is making it seem like you have to take as much time as you need, close an eye and see if that helps if not close the other, close both eyes for a second and open them together, squint, blink a lot, blah blah blah. Different things work for different folks, try them all lol. Oh and supposedly the outside circles are never the ones to pick. I believe for SNA you need perfect scores on this test, do some research and see what works for you.
Not sure what to tell you about the blood. I know people have trouble with that, but I never have personally so I can't give you tips there. I would honestly google that as well, someone is bound to have found something that works for them. I will tell you this as a warning though, a kid in line ahead of me passed out while waiting in line and smashed his face on the wall. He had to be taken out in an ambulance. DO NOT let this be you.
Maybe go get an STD test, I get one about every 6 months just to be safe and they take blood for that, could be good practice for MEPS.
Good luck!