Personally, I like to use the darkest filter I can that I can still see the puddle and the joint. I use a #12 for most everything. When I weld with FCAW for long periods at 250 amps or better, I find a 12 isn't enough so I use a 10 in the flip-up plate and a 4 or 5 burning plate in the hood (is that a 14 or 15 total?). Again, this is only what I like to use; most people will say it's too dark for them.
I keep my face away from the welding so that heat doesn't distort the plastic cover plate and smoke doesn't build up residue on the hood. Plus I don't have to breathe in all the fumes.
It helps to know what your joint looks like and where it goes so you know what to look for when your hood is down. I don't mean any "may the force be with you" stuff. But if you know what is there and what it should look like, it's easier to track the joint. It may help to start out with a little lighter filter and go darker later on (although your 10 should be fine.). Some people find the gold plated lenses help with visibility.
The biggest problem I see novice welders having is they are watching the arc but not the puddle or the joint. It's only natural to look at the brightest light in a dark place. But it's like driving a car with the sun in your eyes. You learn to look past the sun to see the road. (Or stop if it's too bad)
I would say if you are feeling any eye strain, or seeing bright dots after welding, you probably need a darker filter. Just keep it clean, practice so you know what the view should look like, and relax. Don't tense up and put your face in close unless you have to, sit back and "enjoy the view". Move your head to different positions to see what is comfortable and lets you see.
It also won't hurt to visit the website in the previous post to learn more.
Keep at it and you'll find what works for you.
CHGuilford
i had the same problem you have right now with welding in general. i read all the books i could get my hands on. but for some reason, no matter what i read, no matter how long i practiced welding, NOTHING compared to actually watching somebody else weld who knows what they're doing. and that same person can watch you and point out what you're doing wrong. words can only tell so much, but experience and a watchful eye can tell everything. you can get all the advice you want from these guys...and it's great advice-- i find myself learning a lot...but unless you have somebody to show you what these guys are talking about, it'll be a hard career/hobby to get used to at first.