Lizard heads are pretty easy, really.
1. Draw a circle. It doesn't correspond to any real part of the skull, it's just a place holder for about where the head will be. As it turns out this one was too small, but that's ok, it's easy to correct later (step 5).
2. Draw a U-shape connected to the circle. This will be the snout. You can get a lot of variation based on the general shape. Long and thin looks a lot different than short and blunt. If you were making a dragon, you would use more of a duck bill shape. Don't worry about the shape too much, you will edit this later, but you generally want the lower jaw to be flatter than the upper snout line.
3. Draw the eye ridge. The eye ridge is the real key to making a lizard head. It sits on and covers the top of the circle. You can vary this by making it more curved, or flatter, or sharply angled.
4. Now add an eye spot and a mouth line. The eye sits where the snout, ridge, and circle all meet. The mouth splits the jaw, and the lower jaw is thinner than the upper jaw (because the upper jaw also has the nose). This should give you an idea of what the head will look like.
5. I adjusted the head by making the circle area larger, and raising the eye ridge a bit, also repositioned the eye. Mostly trying for the short blunt look in the original. I could have just made the snout shorter by a pixel, but the head was overall a bit small. This head is looking a bit dinosaur-ish, but it will do.
6. Moved the head and added the neck. Lizards tend to have a neck that sprouts from the back of the head rather than underneath. It's just one of those things that says 'lizard' rather than mammal. For a lizard-man, it is sufficient to pull the head forward on a long and angled neck. The weight distribution is balanced by the tail when standing. Since this fellow is a big heavy, I gave him a huge broad neck rather than a thin serpent neck.
7. Filled in solid colors. The eye gets a deep socket to suggest the width of the mouth (if it was viewed from the front).
8. Adjusted the shape again, making the snout stronger. This looks ok I think.
9. Added some bits like the ears. Lizards don't have much for ears, and big round ears look very mammalian. Small ears that look like little wings will preserve the shape of the long low skull and not detract too much, although they look a bit dragon-ish.
The nose horn is a bit off I think - there's just not enough pixels here to do it well, but I thought I'd add it in. I didn't add in the top knot because it again distracted from the basic shape of the head. A fin on the top of the skull would work ok though. Or if you wanted hair, maybe some sort of fringe or mane.
Oh, I shaded the neck some too to show how that looks. The highlights, eh, not so good.
To sum up, your blue guy has the head of a pig rather than a lizard. The large lower jaw, snub nose, rounded ears all say pig rather than lizard. The good news is that the basic semi-realistic lizard skull is pretty formulaic.
Hope this helps,