You've got a sketchbook. You've got pencils, pens, and leads galore. You've even got the most important things- ideas. But you lack the time, or the real motivation, to get the necessary amount of sketching into your day. How do you go about remedying such a thing?
First off, you need your sketchbook and your supplies with you AT ALL TIMES. There are lots of little breaks throughout even a busy day when you can be doodling. Take advantage of these if you cant afford to make time. Riding in the car (if you're a non-driver) is a great opportunity to get some rough sketching in, just mentally prepare yourself for shakey results. The goal is to get those ideas onto paper, a sketchbook is not for perfection. You don't have to lug around a 9"x11" sketchbook like I do, a simple little spiral bound notebook slips into a back pocket neatly.
Second, modify how you think about drawing. Don't aim for finished pieces, go for the gesture. Get down the relevant information, you can finish it at a later time. Consider carrying a camera with you, or utilizing the camera on your cellphone if you need to capture a lot of information in a short amount of time.
Stop being self concious. Believe me, the majority of people in this wide world do not care that you are drawing right this instant. Don't be obvious if you're drawing a particular person if you can't handle attention.
Prioritize your drawing. If this is what you want to do with your life, then give it time to breath and grow. Give up those videogames, cut back on those novels, and dedicate yourself. You aren't gunning to become a professional videogame player or a professional book reader, you want to be an artist! Even if you DONT want to draw for a living, if your art is important to you (as a hobby), you need to dedicate time to it. You aren't an artist if you never draw/paint/sculpt/print. Stop making excuses.
If you are the type who MUST finish a drawing, give yourself all day to do it. Pick at it in little bits.
If a notebook isn't handy, draw on whatever's available. Napkins, the back of business cards, receipts. Draw with a ballpoint pen, a china marker. Be less picky about your materials. I worked a summer as a desk monkey, and I scripted out a comic on post-it notes. Sketches do not need to be archival.
Set concrete goals. If you're really having trouble motivating yourself, promise yourself three full pages every day, no excuses. Set a schedule and STICK TO IT. Bribe yourself. Disconnect the PS3, turn off the internet.
The only person you have to convince with your sketchbook is yourself. Give yourself permission to fail, to try something new and totally falter, to nose dive into horrible. It's a sketchbook. Don't buy Moleskins if you feel weird about messing up the pristine pages. Heck, don't buy a run of the mill, Strathmore spiral bound yellow cover sketchbook if you feel like you have to produce something amazing. Buy a ream of crappy printer paper, a three ring binder punch, and a binder, and use THAT as your sketchbook. Use looseleaf if you have to. Whatever it takes to get you drawing. If having an audience motivates you, start an art blog. If you need criticism, directly ask for it on Twitter or on your blog.
Stop breaking promises to yourself. If keeping a sketchbook is important to you, get to it.
Excuses are what you make when you aren't making art.