Okay so I'm going to try my best here.
My favourite thing to do in art is to paint and draw portraits and I think I'm pretty good at it so I would like to think I can help you out.
I have used a few methods when it comes to drawing portraits. Usually I like to just draw freehand and work out all the proportions and shapes for myself but the grid system works perfectly fine.
Here are two examples of my work, one using the grid system and one drawn freehand.
Rufus by ~Cinnamonster on deviantART This is Rufus. He was drawn using a grid. I used different techniques to shade as well - worked in layers, blending and smudging with tissues and cotton buds, kneadable eraser to get fine highlights and etc. It's smoother and softer overall.
Hugo by ~Cinnamonster on deviantART This is Hugo. He was drawn freehand. The achieve the shading in this I did not smudge any of it, just different pencils and pressures in certain areas. Although drawn on the same type of paper the technique just looks rougher.
Now the grid system is great if you want to make sure that the proportions are EXACTLY as they are in your reference photo (it's best to make sure it's black and white because when you come to shading you'll find that a black and white picture is much mroe helpful than full colour). With the grid system I find it easier because you can open the photo into the photoshop, print it out at the same size as you want your drawing to be (I hardly ever draw anything past A4 so this usually works fine for me) and you can draw the grid over the printed copy and the grid on your page will be exactly the same size and easier to compare with the reference. You probably need about three different sizes of reference pictures (well, I do at least) but let the largest be the one that's the same size as your drawing. I did this for my Rufus drawing.
Freehand drawing is a bit more complex but I find it more fun. You probably need about three copies of your reference picture again (also black and white). This kind of drawing requires a bit more thought than the grid system. You need to work out angles, parallels and stuff like that (I, for some reason, call it 'working mathematically' *shrug*). Take a look at Hugo. I'm going to use his eyebrows and nostrils as an example. See the inner end of his eyebrows? See the beginning of each nostril (from the outside of the nose)? Notice that his eyebrows end just before his nostrils. That sounds weird. Okay maybe if you drag your cursor down from the tip of both eyebrows and you see that you reach the beginning of the nostril. Also notice how the corners of Hugo's top lip form a neat, symmetrical trapezium sort of shape with the corners of his nostrils? You need to pick up things like this when you check out your reference picture. There are hidden shapes and angles and lines in faces which, when you discover, help you to draw the basic outline much quicker and more accurately.
Shape is incredibly important. You cannot move onto shading once you have proportions correct. Spend a bit of time studying your reference picture, work on the shape until you think you've got it perfect. It's also important to mark out extremely lightly where the shadows are supposed to go. Never draw the lines too dark as you don't want them to be noticed once you start shading. This, I assume, is supposed to be a realistic portrait.
With tone you just need to be really patient. Finding out where the light is coming from in your reference picture can help. I'm not sure how to talk about tone because I've just picked up on it over the years. Try looking at works by Vermeer. He has been described as a 'master of light'. Consider the way light falls on people's faces and just on everything in general (even when you're walking home from school or something, just notice how light works to create and emphasise shape). There are so many ways to capture light when drawing. Personally, I just like to use different pencils and pressures rather than smudging but that's just me. Others use crosshatching (I'm not a fan of this as I cannot do it very well but it works effectively if you can manage it). Find what works best for you and work with that. If you like to smudge the graphite then things like tissues for large areas and cotton buds for smaller areas are great instead of just using your fingers to smudge. If you use your fingers you could risk getting your page dirty and leaving finger marks on it whereas the tissues are smooth and leave no marks. When smudging work in layers. Look at Rufus. The fur coat is pretty dark but has ighter parts showing through. What I did was put down a layer of very light graphite, smudge it so it was smooth, then went over it again in certain areas with a couple of layers of 4B, blending with tissues each time. To achieve the highlights in both the fur and his hair I used a bit of kneadable eraser wrapped around the edge of a toothpick. You need to
carefully (I place emphasis on this because you really don't want to scratch the paper) drag this through the dark layer each time to produce each strand of hair/fur. The same effect can be done using a sharp pencil (preferably 4B) to create darker areas. Drawing hair has always been a pain in the neck for me but I found this technique helped alot with the drawing of Rufus.
Last piece of advice from me is that you should probably get a nice set of pencils. I like Derwent Graphics. It's also wise to buy a kneadable eraser. They're really great if you need to erase something really small and also if you like smudging. And don't draw on crappy paper. Get a sketch book with some good quality paper. You probably know this anyway but I feel it's always a good thing to add anyway.
Hope I've helped a bit. Feel free to ask me anything else. I don't mind
Here are some tutorials from a talented girl on Deviantart if you need more help/advice:
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