What's the first thing you should do when you pick up your guitar? Well, you don't need me to tell you, because you know. You should check the tuning. It's a rule that I broke most of the time back in the day when I was first learning. I'm sure I must have made more of an effort when I was playing with a band or jamming with friends. But for sitting around in front of the TV, just practising licks, bends and scales, I would give the tuning just a cursory check.
These days, I try to be more disciplined. After doing five or ten minutes of hand and finger stretches (more on that later) the first thing I do when I take my guitar from its stand is grab my little clip-on tuner, attach it to the headstock and start tuning. It's a good habit to develop on a number of levels, not least of which is that it trains your ear to appreciate what your guitar should sound like when it is in tune. And the more you do it, the more attuned you'll become to a well-tuned instrument, and the more you'll recoil in horror when you hear one that isn't. With so many tuners available for all tastes and budgets, it's an essential piece of equipment that you can't afford to be without.
One of the more versatile types of tuners on the market today is the clip-on variety. With a strong spring and a lever they can be quickly attached to and detached from, your guitar's headstock. And they are small enough carry around in your pocket in case you suddenly find yourself in a situation where you have no choice but to play. Urged on by your friends to join a Sunday afternoon blues jam at a pub far away from your home is the kind of thing that springs to mind.
So, if you have a tuner, please use it; and if you don't, please get one as soon as you can. Get tuning. You'll thank yourself for it later.