Below is a step by step of how I created this turnaround model sheet for my Luchador character, I hope it helps.
STEP 1 - Rough Front Facing Sketch
For the first step of the model sheet process you are going to need to establish the front facing body pose, this should be very basic and show no real personality. This should be a relatively loose image there is no need to create tight lines at this point. I like to draw in a different colour from black at this point but that's just personal preference.
STEP 2 - Creating Duplicates for Costume design
For the next step you will need to duplicate the image you have just created, as the next step will be costume creation. Simply copy and paste the layer multiple times, you can do this as many times as you want, in fact the more the better, but for the time being I have just done 3. Merge the 3 layers into 1 layer and name it 'base roughs' then lower the opacity and lock the layer.
STEP 3 - Costume Design
Now you will need to create a new layer and name it 'costume roughs', make sure this layer is above the base roughs in the layer tab. This is where you will get to explore different designs for your character.
With your costume roughs layer selected you will now need to illustrate several different costume designs for your character. As before there is no need to be tidy at this point, these can still be rough designs as we will tidy them later.
STEP 4 - Removing the Base Layer
This step is a simple one simple, in the layer tab simply hide the base roughs layer. You now have your first rough designs of your character and will now choose your favourite design.
STEP 5 - Choosing your Favourite Design
Once you have chosen your final design you will then need to select it using the lasso tool, once you have selected it you will need to copy and paste it into a new layer, name this new layer 'final design rough' and move it over to the left of the screen. You will also need to hide the 'costume roughs' layer.
STEP 6 - Guide For Final Lines
Once your character is in position to the left of the screen you will then need to lower the opacity and lock the layer, this will now work as the guide for your finished line work.
STEP 7 - Final Line Art
The next step is to create a layer called 'final line art' this is the layer we are going to use for our finished drawing, make sure this is the top layer in your layer tab, it needs to be above the 'final rough design layer' be sure to use a brush with a harder edge if that's the style you're going for.
STEP 8 - Colour (optional)
Now create a layer and name it 'colours' once you have done this you will need to colour the layer with a flat pencil brush as it makes it easier for colour selection when we do colour variants.
STEP 9 - Colour Variants (optional)
Colour can add a great deal to your character, so it's always a good idea to play around with variant colour ideas. Duplicate the final line art and colours layer as many times as you'd like and then select different colours using the selection wand and create several alternative ideas.
STEP 10 - Model Sheet Guide Lines
If you have created the colour layer simply hide it for now and create a layer called 'Model Sheet Guides', you will now need to create several straight horizontal lines from various body points to make sure your rear and side view's line up. Once this is done, lower the opacity and lock the layer.
STEP 11 - Rear and Side View
A helpful way to speed up this process to create a copy of the front facing pose, flip it horizontally and remove the internal lines you can the create the back view from the outline you have knowing it will match up. Or you can simply follow the steps as before and rough out the figure first.
STEP 12 - Final Flat Colour and Finished
At this point I like to add me chosen colour design to all three pieces and hide the guide line layer to give it a nice finished look. And that's pretty much it.
There are multiple ways to do character design sheets, this is by no means the only way. In fact here is a link below to 2 great videos. One on character design and one on creating a model sheet.
Character Design -
Character Model Sheet -
Also here is a great link to an expression sheet - http://napalmnacey.deviantart.com/art/25-Essential-Expressions-55523083
I hope this has been helpful, and if you have any questions or requests please feel free to comment below.