...I can help you with that. Once upon a time, I was developing a class of Uses for Leftover Handspun Yarn but it never really got off the ground--too little time in my schedule. And you're about to benefit from the notes I made!
Obviously, gauge and yardage are big considerations. Sometimes you'll have enough yardage for a whole item. I like to use Ravelry's data base, using the Pattern Browser function. Simply click on the attributes you know, like knitting or crochet, yardage, yarn size (DK, worsted, etc.) and see what comes up. You can fine-tune the search by selecting accessories or baby things--it's great fun to play with pattern ideas that way. Try knitting a tea cosy, perhaps even felting it for extra warmth. If you're like me, it's takes an hour or more to consume a pot of tea and having a cosy on the pot keeps it nice and hot. And your tea can keep you company while you browse more patterns on Ravelry....
Have lots of smaller skeins? I consider these design challenges; how can I combine colors and weights and yardage to make something special? (This is why I sell my Bits & Pieces sets in my Etsy shop--there are lots of creative people who need just a bit of certain colors.) Play with combinations of yarns, let them sit somewhere where you can see them daily, add a yarn/subtract a yarn each time you pass the grouping, and soon you'll have a coherent group of yarns that can be used for a garment or accessory. Try a lengthwise fringe scarf--see my Handspun Delight pattern on Ravelry, it's free for the downloading.
Striped hats are another good use of small skeins; just use your favorite hat pattern and alternate yarns in skinny or wide stripes throughout. Both of these were made with a mixture of small skeins of handspun and commercial yarn.
What about using those smaller lengths in a widthwise sampler scarf? Knit or crochet in a stitch you haven't used before until the yarn is finished, maybe do a few rows with a shorter length, then start a new stitch with a longer length. It will stretch your stitch knowledge and creativity. What about a diagonal scarf with stripes of different handspun yarn? Knot the ends at the edge and let them hang out for a touch of funkiness.
Making a solid color plain cardigan and want to punch it up a little? Pick up the neck and front edges with a single row of handspun in a pleasing color, then continue with the solid color. You could also add a row of the same handspun just above the cuff ribbing. Use your handspun to duplicate-stitch a little motif on that sweater and you've created a special piece that no one--NO ONE--else will be able to make.
It may be yarn and we all may be making garments, but that doesn't mean yarn can't be used like paint or colored pencils to create masterpieces. Try using some handspun in these ways; let your mind and skills take you some place special. Handspun yarn can push your creativity to new levels!
And please feel free to post photos of your work here, I'd love to see what you're doing.