Knitting hats can be difficult without the right technique. Traditionally they were knit flat and sewn together, which if you weren't careful would result in a seam which was either visible or uncomfortable. The latest techniques call for knitting hats in the round, either using double point needles, which can be a handful, or my preferred method, magic loop. It still surprises me how many people have not tried this simple technique. Magic loop uses a fairly long circular needle, say 40 inches or so, and placing the stitches on the two needes, and on the cable. The cable acts like one to three double point needles except that the stitches can't fall off:-)
When working a hat or large item pretty much all the stitches can be placed on the needles, as you work towards the crown you need to have fewer and fewer stitches on the needles, and more on the cables.
The technique is great for hats, like the new Ivy Brambles Watchman cap above, and for other items like neck cowls, such as the Diamonds Galore Cowl below.