There's a few ways to change up your faces.
The most obvious is doing some caricatures. This exercise is pretty good:
http://cartooncave.blogspot.com/2010/10/...types.html
What you do is use a video or tv show and draw characters based on the people in them. Personally I find it's best if you watch something you have no interest in or drawing from TV that someone else is watching, so that you don't get too distracted :v
Another is drawing random shapes and drawing faces to fill 'em. There's a few of those here as a starting point (although I imagine you're quite capable of drawing your own squiggly shapes :v ):
http://design-a-character.deviantart.com...y/24434896
A useful thing here is, once you've filled a shape, try and draw the same head from a couple different angles so you can get a feel for an overall design.
Last one I can think of: FURRIES LOL.
Okay, not really, but drawing characters based on animals can be helpful. Start by drawing a few sketches of the animal's head, and then try to draw a human based on that animal.
Say if you're looking at a piglet
you'll probably end up drawing a kind of rounded face with an upturned nose
if you're looking at a bear you'll probably end up using big strong lines and squarish shapes to make a big scary looking dude instead
not sure if I'm explaining this last one all that well x:
You'll probably find that bar the last one, your resulting drawings will be sort of exaggerated and cartoony looking, so you'll probably have to do some more work to apply the lessons learned to your own style.
I thought of another one!
You could look for more subtle changes if you try comparing actors who tend to play vaguely similar roles or have a similar look
So, as an example compare Clive Owen, Gerard Butler and Javier Bardem (so manly) and look for ways that they differ. All three of them have sort of similar squarish face shapes, but look for what makes them distinct and try to draw a similar set of characters.
And another one!
mess around with gender. Seriously. Try to draw a woman who still reads as a woman despite having a few traditionally masculine characteristics, and vice versa. Even try drawing someone fairly androgynous. This one can be a bit harder since you'll find people will tell you it looks off when it isn't, because in drawing people tend to be kind of used to seeing fairly idealised features, especially with women x: