Check out this book as well.
It’s sounds remarkably like the answer to my question is the same as to, “How do you get to Carnegie Hall?” 
Which is actually encouraging, because I’m a very persistent sort when I set my mind on something – if all it takes to improve is spending time at it, then improve I shall.
Also thanks for the recommendations on books – I’ll pick them up and start in.
Here’s yet another vote for Betty Edwards and Drawing on the Right Side of Your Brain. I took an adult education class some years back which used this text. I was one of those kids who drew better than most of the class when I was in grade school, but I had done little or nothing since. (I am in my forties). I found that there was a pronounced improvement in my work after taking the course, which was short and very informal, and I had a lot more confidence besides.
I had been suspicious of Edwards’ book to start with as the right brain/left brain business seemed like a loose generality developed into a gimmick. Edwards herself admits that the right-left distinction is something of a generality however.
She uses the right-left distinction as a metaphor for different habits of thought which can be employed while drawing. Central to her book is the observation that people who are awkward and uncomfortable with drawing tend to identify objects, and then draw symbols for those objects, while an accomplished artist concentrates on observing and mimicking specific lines and contours. For instance a child–or an adult who still draws childishly–will draw an oval or a circle with a dot in it for an eye, while a portrait artist will try to draw the contour of the upper eye lid, the position of the iris, etc.
It is highly questionable whether one can become an accomplished artist solely by taking the right instruction; there is probably ultimately no way of proving whether there is such an innate thing as talent or not. Techniques such as the ones Edwards teaches, however, can be extremely useful in teaching a person to copy what they observe accurately however.
It is interesting in this context that Maxfield Parrish, one of the most successful oil painters of the 20th Century, and a man who could render scenes with breathtaking realism, said that he felt he could not actually draw well; he is said to have only been able to come up with a crude and clumsy scribble when asked to draw something spontaneously. He could, however, copy from life or a photo with photograph-like precision after dividing a canvas or a sheet of paper into small squares, a technique Edwards teaches.
Practice, practice, practice. I can’t stress practice enough. I represented my High School as their sterling scholar art student (I’m not sure how many states have the sterling scholar program but it is statewide where I live). I still have drawings that I did when I was 4 years old. Trust me when I say that they look like the drawings your typical 4 year old would make. If you look at the progression of my art over the years you can easily see a divergence in the work from the average of a person my age (i.e. at 6 I was a bit better than most other 6 year olds, at 10 I was a fair bit better than most other 10 year olds, at 12 I was quite a bit better than other 12 year olds, etc.). What’s the key? Practice.
Grim
In your original post, you said that you would love to sit and “sketch” etc… The split brain theory will not allow you to do that.
People who can do that- are already doing it ( un-able to NOT do it !).
ASin driven to do it!!! usually from early years.
AND as others have said-- they do it A LOT!
I taught The Split Brain Theory (and also added tecnique to give a photo-realistic look) for several years as a private teacher with classes as big as 6 at the most.
ANYONE— willing to put 3 hrs of drawing homework in per week- would end a 6 week (1 1/2 hr. classes) set of classes doing portraits .
Most unbelievable.
I was able to teach anyone who could read (my youngest 10, oldest 70 ) to draw realisticly. THAT— is very different than “being creative and being able to draw from memory”
PS… My BEST students were married mothers with jobs-- do you know why ?
Geno
Someone mentioned Burne Hogarth’s books…I definitely recommend those by him to everybody especially Dynamic Figure Drawing…that book has made me improve my forshortening of the figure much better and more impressive. I’m an artist and currently an art student studying illustration and animation…the key is not really talent, but practice and persistence. Take criticism constructively and not personally and never, and I mean NEVER, listen to what non-artists say about your work…they don’t know crap. lol. “ooo such good shading”…but my figure looks like it was in a train wreck!! lol. non-artists are impressed by the “tricks” of drawing, whereas artists are much more impressed with the fundamentals of observation. Remember that. Key to being an artist= observation of how things really look. that is one of the hardest concepts to grasp in art and it took me several years of art school to fully grasp it. So don’t get too uptight if you don’t see results quickly (i’m not necessarily a big fan of edwards for that reason…the initial improvement is just that…initial, your goal should be to always improve). As for people who seem born with an innate ability to draw…well, that is probably more an innate ability to observe. Lastly, have fun with it…that’s what art is all about: expressing the things you want to express…
You already know how to draw–you just need practice, like everyone else has already said. My suggestions: carry a sketchbook all the time and draw whenever you get a chance. Find a photo in a magazine and sketch it. Anything, as long as you’re trying new things and having fun with it.
Classes are a great idea, and unless they have prerequisites, don’t worry about not having enough experience to take them. You could also check with galleries or with the artists’ guild (or other group) in your area; they will sometimes offer classes in a particular technique and give you a chance to work a little more creatively.
Also, don’t worry too much about how close the final product is to your original vision. I’ve done very few paintings or drawings that have looked like my initial sketches. They tend to evolve as you work on them, which is part of the fun.
Enjoy!
Real-Life High School Theater!
Me: Mr Art Teacher, could you give me an idea of what I’m doing wrong?
Teacher: Well, Mike, some people have talent and some people don’t.
Gee, I wonder how many of those “talented” people have been supporting themselves with their drawing? So, yes, people with no talent can learn to draw.
Another vote for Betty Edwards. My goodness, she’s wonderful.
And, I was really impressed with Keys to Drawing. It covers similar things to the Edwards book, but in a different way. If you could only get one book, I guess you’d best stick with Edwards, but really, the Keys to Drawing is just wonderful—in a different way.
Also, as others here have emphasized, practice, practice, practice. I loved drawing as a kid, and so I practiced. I saw other kids my age, equally “talented”, but they didn’t practice. Guess who ended up having more drawing skill after a while?
This is SO true. Believe it. I’ve seen it, I’ve lived it. “Talent”, while a nifty thing and not to be dismissed, is not the real determining factor here. Not giving up is the main thing.
Another vote for Burne Hogarth, but possibly for later on, after you have been drawing for a while. I love Hogarth—he was one of my teachers at art school! 
(No, really, he was! For two semesters.)
Now i’m jealous. lol. punk.