just drawing will never get you all the way. it is really really important to read books and then try out those techniques, and to do exercises. books is whatever you want just always have one you are working through.
personally, i think art education should be more exercise based. including a lot of very simple exercises regarding basic mark making and shape creation at the early levels of learning. this is very unattractive to most students of art because it is extremely boring, and the end result is not a badass robot ninja or whatever.
however what i am talking about does yield results. by studying the absolute basic skills of drawing, you will develop the muscle memory you need to be fluid and accurate, and you progressively get more control over the ability to create lines and shapes. the idea is to build good habits regarding the basics of drawings, so you don’t have to worry about simple mistakes you should be avoiding.
all of these can be done with a timer very quickly. try and really focus on the simplicity of what you are doing to help build focus into your drawing habit. set it to two-five minutes and:
Draw from the shoulder: put time away every day to practice drawing from the shoulder. don’t just try and do it as you free draw, make time to specifically practice drawing from the shoulder. you can stop once it is second nature.
Straight line exercise: Draw two points more than a hands length apart, before applying pencil to paper “ghost” the connection as straight as you can, then try and make a straight line connection. Do this quickly and repeatedly for the set time. variations: length, angle, try and make an exact copy of the previous line, incorporate cross-hatching practice, etc.
Corner Exercise: make corners repeatedly. try and vary heavily the direction you move your pencil to practice mark making. work from the shoulder. try and make perfect points and angles. similar to straight line exercise.
Basic shapes exercise: Squares, triangles, ovals. pick one, do it over and over and over for the allotted time. variations build new shapes from only the three basics, make small shapes, and make huge shapes.
Ellipse exercise: this is the same as the Basic shape exercise but ellipses are so important i though i should mention it twice. vary shape and size and angle, length, width, etc.
proportion exercise: take any above exercise and vary it by finding relations and proportions. example: when doing square exercises, make a rectangle, then make a second which is exactly 1/6 as long. or 1/2. or 1/8 the length. or exactly double in size. you get the idea. use measurement techniques (pencil tilt, “count heads”, etc). variation eventually this exercise should go into the real world. sit at a desk, and see how many cars=one building then draw that relation. be creative.
contour drawing: draw and draw the silhouette of an object. this is a common one but it is one of the best. try and imagine you are “touching” that contour as you go.
Mark making 101: grab a tool, and see how many different ways that tool can be applied to a medium. just play. see what it can do. hold it in a funny way smash it. whatever, the practice repeatedly any interesting results. learn to control how you make that mark, then use it later.
i suggest getting a sketchbook dedicated to only these simple exercises, and spending time on it every day. you don’t even need to get worried about it not being a good drawing time, because you really aren’t shooting for quality, just building good habits.
the more you do this stuff the more basic control you will have, the less time you will be frustrated when drawing because you fucked up a corner, or you get the proportions wrong, or you can’t draw that line or whatever. the army trains cadets repetition until the basic skills and behaviors are second nature. what i am advocating is exactly the same thing. you want the easy stuff to be second nature. once these mechanical skills are developed, you will have more basic control over what you can do, then you can start to bend the rules and get very creative with how you see and perceive, because you will have mastery over the basics of reproduction, and will execute those skills with ease.