I am in no way an expert when it comes to illustrating. I haven't had any formal training or majored in art--I just love using it as a way to express myself and a way to escape from reality when needed. If you are looking to teach yourself how to draw-here some steps you can take to point you in the right direction of being a self-taught artist.
1. Choose your medium
Decide if you are going to use a sketch pad and pencils, watercolor or markers, or if you are going to go digital with the use of a tablet like the iPad or Wacom. I can speak to using both a sketch pad and iPad as I currently use the latter for all of my illustrations. When you are first starting out-it's perfectly fine to use the traditional sketch pad. This is a good way to warm up with practicing facial dimensions! If you decide to go the digital route-please account for expenses such as the tablet, pencil and whatever program you will have to download.
2. Digital Software
If you decide to go the digital route via an iPad- I recommend using Procreate. Procreate is very user friendly and having used it for the last 4 years I can attest to how easy it is to start using. I have also used other programs: Krita and Adobe Illustrator when I digitized my drawings on my PC; on the iPad I also tried to ClipStudio Paint and Autodesk Sketchbook. Photoshop is good for touching up your illustrations-unless you decide to go the vector route you can use Photoshop all the way. However, Procreate has remained my favorite. You can download brushes as well as customize your own brushes. There are many tools to help you get started with Procreate as well. As stated before--I can only speak to what I know-hence why I love using it.
3. Where to start?
If you are interested in drawing human characters such as I when began illustrating-the best way to practice is starting off drawing figures. You can search for reference figures or poses on Google or Pinterest and find a ton of resources on basic figures to practice drawing. As far as facial illustrations (portraits) Youtube was a great tool with helping to divide the face into 1/3s. Paying attention to the anatomy and spacing of the human face is important if you want your drawings to look close to realistic. You don't always have to draw a full face or sketch--just spend time sketching parts: noses, eyes, lips. You will come to find that you have your own style of how you like things.
4. Finding your own style
When you first start out drawing- you are trying to build your own brand-one that is recognizable by looking at a piece of art. It takes time to develop as you learn and challenge yourself with new techniques and skills. Don't compare your style to the next person---everyone is different. Please do not be hard on yourself--this took me some time to learn (and still learning).
5. Practice with tracing
I've seen a lot of people recommend tracing when first starting out. I have nothing against it, however this may handicap you in the long run. Don't trace more than a few times as after all the gift of the process is learning and developing your skill not handicapping your potential talent!
I hope these tips helped- as my whole journey has been trial and error. Along the way the main thing that has helped me was and is challenging myself to learn more and refine my talent. Don't be afraid of a little challenge.