Practice is leet ! First of all in my opinion I'd say get a good fundamentals book to help understand what your dealing with, start off with still life images in black and white to help you understand gradients in lights and darks, get a good pencil set! from around 7H to around B6
and get some blending stumps to.
Use grid lines for starters to layout your drawing , sketch like crazy (remember) sketches are not your final masterpiece they're just for exercise and to help you understand what your doing, and or just for fun.
When you are drawing think of the shapes and angles you are looking for, squint your eyes now and then to blur things out it makes things pretty handy.
Start out with less complex images and things and as you progress you will scale things up, step back now and then so you can see your full image then you can say "hey.. that looks a bit off" then you can fix it.
don't go for shading right away, work your layout first then throw in a few simple shadows to indicate the dark spots where it's most needed.
One of my favorite books for overall drawing is : Giovanni Civardi's complete guide to drawing.
Drawing is like learning how to play an instrument, you can't just pick it up and do a master guitar solo, you need to practice your ABCs and work your way up, it might be hard at the start but as you progress you will love what you can create as you get better and better.
Tip:Tryout different mediums too! Pen and ink, markers, paint, pastels.
Start with using only one color and it will help exercise your sense of lights and darks.