Sock yarns come in all guages, fiber types and colorways.  Picking the sock yarn that will produce the socks YOU in particular like to wear can be a challange.  Here's some easy guidelines to help with your selection.

First - do you want to be able to wash and dry your socks in the machine along with the rest of your laundry?  If so, make sure the sock yarn you buy is SUPERWASH.  This means the fibers have been coated to keep them from felting.  Superwash items can be treated just like your regular laundry.  The washer and dryer won't effect their size or shape.

Second - weight.  Do you want fine guage lacy socks?  Hiking socks?  Really heavy warm socks to wear skiing?  How thick and durable do you need your socks to be?  If you want fine guage socks to wear with your regular street shoes, you want to look for lace-weight, sock-weight, or fingering-weight yarn.  The finer the guage yarn the more intricate the design you can incorporate into your socks.  Remeber to buy enough yarn for both socks, if you're getting hand-painted yarns.  For fine guage socks you need atleast 440 yards for 2 socks.

If you want hiking socks, or even thicker socks, you can knit with worsted weight yarn  Make sure you get the appropriate size needles, size 6 - 8 US.  You need to knit with smaller size needles for your socks, because the wear on the bottom of the sock is greater than on any part of a standard garment.

Very warm socks can be produced by using the double knitting technique...  Or knit the inner liner, and then turn it inside out and knit the outer sock.  If the inner liner is knit with angora, alpaca or cashmere, the socks will be VERY warm.

Thirdly, consider what style socks you want.  Lace, Fair Isle,  Kilt Hose???  Crew socks or knee socks?  The style sock you want effects which type yarn you buy.  Fair Isle socks knitted with worsted weight yarn may end up like a pair of boots!  Too thick and stiff to wear.  By the same token, if you want heavy duty hunting socks that will help keep your little tooties warm while stalking that buck, firmly knitted knee socks would be just the thing.

Fourth - color.  Hand-painted multicolored yarns are very lovely.  But if you want a lace pattern to show, you need to pick a hand-painted skein that isn't overwhelming.  You'll be knitting lace that you just can't see if the colorway is really dominate.  I'm not saying all your socks need to be a single color.  I just want you to think about how the color you pick will complement or clash with the design you have in mind.

Fifth consideration is fiber.  While I did emphasize that superwash is a requirement if you want to be able to machine launder your socks, what fiber your socks are made with is equally import.  Superwash is available only in wool or wool/nylon blends.  If you don't want wool socks; cotton, alpaca, even silk also make lovely socks.  Understanding the fiber characteristics will effect how your socks wear.  Cotton and alpaca have no "memory".  They "grow" when they are warm.  If you don't knit you socks firmly and incorporate a ribbing in the cuff your lovely handknit socks will be slouch socks that won't stay up.  2x2 ribbing or carrying nylon along with the sock yarn in the cuff will solve that proplem.

I have 25 pair of handknit socks.  I love knitting socks and find that handknit socks really let someone know I care about them.  I've probably knit 100 pair of socks in my lifetime.  I carry a pair in my purse to knit on whenever I'm waiting in line...  You might not be that avid a sock-knitter, but I hope you enjoy each and every pair you knit.