Right this is how you should go about getting your heads correct;
Here are some examples of head studies, your new best friend;
Right look what I did, first of all I concentrated only on the form, making sure to get them correct and only putting in brief indications where eyes and stuff go. Also note that there are many ways to draw heads so make sure to practice different head styles as well. I also make sure to try many different angles, unless you have particulr problems with one angle then make sure to do a variety of them or you will find you won'tbe able to draw heads at the large variety of angles that we as humans can put out heads into.
After doing that quite a number times and making sure I was happy with the head forms I then made a couple more and this time put in detail trying to make sure placement was all correct but at the same time paying attention to what I had learnt previously. Also practice accessories and different head styles again as this will all effect the final outcome. Then I post them up, get feedback and repeat.
You may have noticed that I have done this a couple of times in the past couple of weeks and the reason is because I've only just realised that the heads I drew had several problems. Now I continue at least every week to do a head study because even though in manga anime style the heads are simplistic compared to anatomically accepted heads, they still have their own respective complexities which do require working on. Now, i've only had about three major head studies using that procedure and the amount of detail and form of the heads have improved is astronomical compared to when I begun, still lots of room for improvement but they are getting somewhere. Try this and your problem will begin to iron itself out. They can also be fun exercises if you want them to be a good example is how Rei draws heads (provided in the spoiled section), they are amazing, why? because he practices them constantly xD and I think you would benefit from doing the same
Also practice drawing nice flowing straight lines out on paper or on whatever CG format you use. This will help make you more confident in your line work.
> Use references if you require them to be able to visualise how the neck joins to the head and just to help with angles etc.
> Really make sure to post them up, it's the way you can identify you're mistakes so you can concentrate and fix them.
> Don't use my heads as reference, they have many flaws, especially long necks... keep doing that >.>'
Hope this helps
Edit: Thanks Rubisko ^_^ changed it now