The problem with coned yarn is that it is normally very fine - it is, after all, designed for use with knitting machines, not for hand knitting. A lot of cones are very large too - some of these weighed around the one kilo mark. In my experience, the best way to use it when working by hand is to put several strands together. So I set out to crochet a blanket using four strands of yarn at a time with a size 6.00 hook.
I chose 2 different combinations of yarn, and made each granny square 12 inches by 12 inches. 24 squares were joined together using slip stitches to make a blanket 6 feet by 4 feet:
To edge the blanket I did one round of dc in the paler combination, then one round of crab stitch (AKA reverse dc) in the darker combination.
The blanket weighs 1.4kg and is very warm (that's said with feeling, having had it on my lap most of the day while I crocheted the border and darned in all the ends!).
And despite using 1.4kg of yarn, there is still an awful lot left on 3 of the 5 cones I used! At least 2 were almost completely used up. Now I need some ideas for projects to use up more of the cones.