I was asked in a comment about needle size for patterns, and in particular, for the ribbed mitten pattern I posted about a month ago.
The simple answer is that for a yarn (or yarn combo) that knits up to a gauge of about 3 st/in, a needle size of 9-11 (5.5 mm to 8 mm) is the usual recommendation.
The longer answer is that it depends.
I am a very loose knitter, especially compare to the standard charts of recommended needle sizes. So a size that works for me won't work for everyone else. Thus I hesitate to recommend a needle size when I write out my patterns.
Also, I don't usually specify a yarn. I might use handspun, or some ancient stuff from the leftovers bin, or something where the ball band was lost years ago. I might strand two or more yarns together. And so on. I do try to give a general gauge and/or a finished item size that you might want to keep in mind. Where possible, I try to work in measurements (knit until item is X inches long) rather than gauge (work X rows). I also try to give a sense of how accurate your gauge needs to be.
Most of my patterns are more in the nature of concepts and methods, basic generic plans that work for a range of yarns and that can easily be customized to be larger or smaller based on gauge and personal preference.
For myself, I usually try out a chosen yarn with a likely-looking needle. If I like the fabric, it's good to go. I do a rough gauge check, a few simple calculations, and then cast on.
For small items, the item itself is the full gauge swatch. Evaluate after an inch or two. Do you still like the fabric? Does the item fit? If yes, keep going. If not, you haven't lost much time, and you've learned something that will make the next attempt better.
For small items, small differences in gauge do not matter much. For large items, they matter a lot. For larger items, say a sweater, I might start with a sleeve instead of the body. Or I'll go top-down. That way, I can evaluate fairly quickly and make adjustments if necessary without always having to unravel and start over.
I don't know if that helps any.
If you are a new knitter, try the ribbed mittens (or the wristers) with a yarn or yarn combo that falls in the chunky/bulky range and a #10.5 needle. If you don't have a #10.5 needle, try a #11 or a #9. Evaluate after an inch or two and change needle size if you don't like how it looks or fit. With 24 stitches per round, this goes fast. You're not losing a lot of time if your first attempt isn't working out.
If you are a somewhat more experienced knitter, eyeball the yarn or yarn combo and pick a likely-looking needle size to start out with.
My approach to gauge and swatching is somewhat more relaxed than some people's approach. Sometimes one really does need to be excruciatingly careful about making gauge swatches, washing them, and then evaluating before committing to the actual project. Sometimes one can be more cavalier, casting on and then seeing what happens, knowing that minor variations aren't going to change the outcome all that much. With experience, one learns which approach is best suited to which projects and yarns. Even then, mistakes sometimes get made. Which, of course, is how one gains experience. What's that old saying? "Good judgment comes from experience. Experience comes from bad judgment." Live and learn. And have fun knitting your way to wisdom.