A close friend of mine is looking to pick up drawing after a long time, and complained on Twitter, that good advice and tutorials online are hard to come by... and I agree. A lot of artists and pseudo-professionals put out things on how to draw and its mostly a mix of bad advice with good intentions.
So to avoid doing that, and to contribute to some of the good advice online, I'm going to just give you my story. This is what worked for me, pick it apart and do some introspection to see what might work for you.
I was halfway through my senior year in college when I took it upon myself to learn how to draw. It was just after new years, and I was trying to decide what I should make my resolution about, when it just hit me: I've been making webcomics and messing about in photoshop for years, but I still can't draw with pen and paper to save my life... I've gotta fix this.
The next thing I did was look online and for books to help, and all of them gave very detailed, intimidating responses to the questions I was asking. They were either expecting me to be a lot younger, a lot dumber, or way less intimidated than I was at that point. So, rather than following along to what a book prescribed for a budding artist, I decided to take the stubborn persistence and desire to learn from mistakes, which I developed while doing those comics and college radio shows, and put it to work for this.
The first, and most important, thing was to draw something every single day. It doesn't sound hard when you're reading this, or even when you decide to take up that challenge... but when you're crunching for finals and dealing with kidney stone attacks, its a completely other thing to follow through on it. I missed some days, definitely; maybe even most of a week in some cases, but I didn't let myself get down about it. I just started drawing daily again, and refused to feel guilty about taking class and my health seriously.
In order for drawing something daily to even work at that point, I also needed to seriously scale down the scope of what I would draw. So, I decided to focus on everyday objects that weren't that complex or that intimidating: Coke cans, desktop speakers, the TV, game consoles and controllers, my phone, mugs and glasses, condiment bottles... literally, anything I could set down and keep still (or things that I could find that can't move, like benches). That entire first year of drawings is so basic and badly done that it looks like the scribbles of a child at points, but there is a clear progression that happens in it. Perspective started to make more sense, shading and highlights became important, my drawings became darker and filled more of the page as I had more confidence in how to start and what I was doing, and there were less restarts or attempts to fix errors.
That leads to perhaps the last major thing that helped me on the journey to learning how to draw: using pen and paper. For me, a Moleskine notebook and a pen meant two important things: permanence and speed. There was no start-up time to account for or distraction from what I was doing. There was no undo button. There was also a clear record of how I progressed when I looked back through it.
When drawing digitally you can't see how many times you undid things on the final product, but when you erase pencil from paper, you can usually tell when you look closely. When I switched to pen, there was also a difference in the thickness of lines where I knew what I was doing, compared to where I didn't and I pressed more lightly in case of error. There was also no way to trace real life objects this way; anything that was in the book got there from my eyes telling my brain what they saw, and my brain telling my hands what to draw. It also taught me to just dive in and get something on the page, rather than hesitate and be scared by the whiteness of the page. Analyzing the size of the page compared to the object is important at that stage; most of my early work is either smushed or scaled wrong, to fit it all on the page well. As the year progressed, I got a lot better about fitting my objects into the page naturally.
The last thing that pushed me forward was taking an actual Drawing class from a good professor. I did that at a local community college and was lucky in the fact that the Visual Art staff was so good and so dedicated to the students. I took that class some four or five years after my new years resolution, and in that time I learned more about drawing than I had in the years leading up to it. A good teacher or tutor is worth every penny if you're serious about improving. That class took me from an okay artist that had developed a style to hide my lack of abilities, into something more.
I'm still not strong enough to call myself an artist without a voice in my head second-guessing whether I qualify as that. But with time and patience, I can make a pencil and paper do things I never imagined my hands being capable of. And those skills, with a bit of translation and adaptation, transfer over to digital mediums very nicely. I can't imagine doing it the other way around, now... and I wouldn't suggest it either.
I have no idea if this would be helpful to anyone reading it, but this was my story and, at least for me, hearing that is a lot more helpful than reading a bullet list of advice from someone I don't know. Just know this, if you're taking on the task of learning to do any form of art: be patient, don't fear mistakes, and learn to take a critique.
You will learn more from your mistakes than you will from doing something perfectly; without the patience to endure those mistakes, you will never overcome them; and unless you can put your ego aside and hear what someone has to say about your art (whether good or bad), you will never make much progress.
Good luck and may your sketchbook's pages be filled with beautiful graphite and flowing ink.
(A/N-- I plan to come back and add some images from my first sketchbook once I can find it. It's still in a box from the move last year, so once I hunt it down, some of those terrible images will be up, contrasted to things I've done more recently)