1. Learn the basic rules of proportion.
Proportion: (n) how one thing relates or appears to relate in size to anotherThis first tip might seem on the boring side, but like any skill you attempt to master, you have to start with a solid grasp of the basics. Just going off on your own will result in flawed foundations that will come back to haunt you later.
When we first start drawing, the efforts we make are more akin to how we see things than how they actually appear. For example, children draw people with really big heads, sometimes all head. Looking at the basics of proportion analytically will make a huge difference in your artwork.
There are many rules of proportion, but the one's I've found most helpful and easiest to remember are these five:
1. Heads are round or ovoid, but not a perfect circle.
2. Eyes fall at about half the height of the face, the nose falls at about half the height of the remainder, and the mouth is about half of what's left after that.
3. No, people do not have anime eyes. Make them smaller. Usually, about 1/5th the width of the face.
4. The ears generally run from about the tops of the eyes to the bottom of the nose.
5. People have a wider forehead than you think. Seriously, the hairline runs way high. Even if they have bangs, those bangs have to start from up top.
Of course, these are just the rules of thumb (or face). What truly sets one face apart from another is how people's individual proportions deviate from the 'norm'. You can play around with proportion later to achieve faces with unique characteristics. The important thing is to apply this at the start. You will immediately have better results.
2. Gridding... it's not cheating. Really.
Sometimes, gridding (taking a picture and applying a square grid over it, then drawing a proportional grid on your own paper) feels a bit like cheating, like tracing someone else's drawing. But really, it helps you to be more accurate when you're starting out and helps you to get a better grasp of proportion. Not just how things seem to look, but how they really look. And while you may someday want to be able to draw without a reference picture or grid, it's good practice for getting there.
3. Draw people you are unfamiliar with.
This one might seem a bit odd, but trust me it helps. People you are familiar with (family, friends, anyone you see a lot of) are harder to see objectively. You know their faces well, and you and others will be able to tell if something is even slightly off. It's better to first practice getting proportion right on people you are unfamiliar with because a) you won't expect it to be as perfect and b) you can actually see the individual facets of their face and how they fit together. With someone you know, you might not be able to distinguish that at all.
4. Don't be afraid of sucking.
Let's lay this out right now. You are going to make some horrible drawings. You will have sketchbooks full of things no one will ever see. And even if you do make something you're happy with, you may find it looking pretty shabby a few years down the road. This is normal, this is expected. This is okay. The important thing is to not get bogged down by perfectionism. No one has to see anything you don't want to show them. Just make sure you practice and thus make progress.
5. Practice.
So of course, the last tip is simply this: practice. Draw faces. Many faces. Look at pictures. Look at people. Fill sketchbooks with your efforts and eventually, you will improve.
I get told a lot "I wish I could draw well" or "I'm just not naturally gifted" and I always find those comments confusing. While it is true that a certain amount of natural talent or predilection for artwork helps, true skill comes from doing something until you improve. Anyone can draw. You just have to practice and find enjoyment from the effort itself.