In bicycle school, AIR is the first of the "ABC's" you get taught. You're supposed to check the air in your tires every time you ride. In my case, that'd mean pretty much every day. I don't follow this rule very closely, but I have adopted a routine that works well and accomplishes the desired result.
The FIRST THING is GET A FLOOR PUMP! In this regard, I agree with "BikeSnob NYC," here, in concluding that you cannot be a cyclist without a floor pump (that post also explains part of my prejudice against triathletes). I used to use a little electric pump. No more. The floor pump is easy, quick, and portable. It sits right next to Buddy. I suggest you get one, with a gage, that'll pump to 160psi. Get that kind even if you have a cruiser you only pump up to 30psi. It'll take less strokes to get that 30 psi than a lower capacity pump. I'd ignore the dual action models unless they're not more expensive. Those are easier but you're into diminishing returns on your investment. ON THE OTHER HAND, if you read too much "Buycycling Magazine" and have gotten attracted to a carbon body pump, just send me a check instead for half the difference and I'll paint your pump black. It's a FLOOR pump, for crying out loud. I keep a second floor pump at work. It's a cheap Walmart floor pump (Bell) I originally purchased when I discovered about Armadillos and hook bead rims. It's better than nothing, and has occasionally proved handy to have around. I would not want to use it regularly. It would not last. A coworker told me the gage exploded on his.
When it comes to tire pressure, I've been influenced by Jaguar autocrossing, using high aspect ratio concours tires. In that regard, I use the maximum tire pressure provided on the tire sidewall as a starting point. In a Jaguar, you do this so you don't scrub the sidewalls right off the front left tire in the corners. On Buddy or my road bike, in the case of the more highly loaded tire (the rear on bikes), I'll often run about 5psi over that specified maximum pressure. What that means is that on my daily commuter, Buddy, with a maximum pressure of 116psi (8 Bar), I run with the front tire at 115 and the rear at 120psi. Some of you may wonder if I'm courting disaster by running with an overinflated tire. I suggest you read Sheldon Brown's page on tires and tire pressure, here. If you're a flyweight, you might want to run a little lower pressure. If you're carrying a LOT of stuff on the back, you might want to go a tad higher. If the ride is too harsh, back off on the pressure a bit.
Anyway, on my commuter, I rarely check air pressure. I've learned what the proper pressure feels like, and it's part of my Monday morning drill to pump both tires back up to the requisite pressure. It takes between three and six strokes of the pump, depending on whether I lost air when attaching the pump to the valve. If it takes more, something's wrong. Monday's easy to remember.
On Frankenbike, I follow a different routine. Frankenbike has Armadillos, and they don't take kindly to high pressure. I run Frankenbike at 80psi and use the floor pump every few weeks, or if it seems something's low, whichever comes first.
On the road, both bikes also follow a different pump strategy. Buddy and the road bike both carry lightweight pumps. When I commute with Buddy, I carry a CO2 pump (which I now know how to use) and a Topeak pump. I also carry a Presta/Schrader adaptor in my patch kit. In the case of Frankenbike, I do not carry a pump unless I'm going a long way. Frankenbike has Schrader valves and air can be obtained at almost any gas station as long (so, tell me again why "Presta is Besta?") as I have a tube and patch kit along. If I have a flat on any bike, all the stuff above about tire pressure goes out the window. I no longer care about any of that stuff, and my objective is merely to get enough air into the tire so the bike is rideable to someplace I can be pickier about such things. I'll just be extra careful over rough pavement.
Why should all this matter? I don't like fixing a flat out in the middle of nowhere, and especially not out in the middle of nowhere when it's cold and dark and maybe raining. I like to buy bike stuff as much as anybody, but I'd rather not buy things more often than necessary. I expect to get 6000 miles out of my Continentals on Buddy. I think the Armadillos on Frankenbike may survive the next ice age.