Allright,

First of all: that's not bad at all.
Second: f you want to improve there is not that much solutions: keep practicing. If you have the time and the money, take art class and anatomy drawing class. It's hard, it can be boring but it'll help. At least buy a book about anatomy and/or observes people. It'll help to catch great pose and it will add weight to your drawings.
Now or your hair probleme it is the same. First ask you that question (and keep it in mind for absolutely anything related to drawing) How I want it to look like ? Depending on this you might start to have an idea on how you want your hair to look like. Remember that realism is not the only answer. I prefer a good stylised hair over any average looking realistic hair.
Practice with photos to see all the kind of hairdo are existing and how they look like.
Try to see the works of artists that have a great rendition of hair like Kentaro Miura (Berserk),Adam Hughe , Murata Range and many other for a rather realistic approach of hair, but look also to artist and works with a lot of stylisation like what Brian Lee O'malley do in a very simple way or Kosuke Fujishima (Ah! My goddesse)in much, much more complicated manner.

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It's a kind of magic.