Gun cleaning is always an interesting topic, when I talk to new and veteran gun owners alike.  Here are a few tips and recommendations, to keep your firearms in top shape, with the least amount of effort.

1. Clean your guns after every use:  This seems obvious, but the best way to keep your guns clean is to clean them!  More frequent cleaning will keep your guns in better condition, combat rust, and reduce operating malfunctions.
2. Get a Boresnake:  The Boresnake is a great, "why didn't they think of that sooner?" item.  Available in the original Boresnake, or the deluxe Boresnake Viper, these are hands-down the fastest way to clean the barrel.  As the manufacturer says, "One pass loosens large particles, scrubs out the remaining residue with a bronze brush, then swabs it all spotless with a cleaning area 160x larger than a standard patch!"
   
3. Stay away from corrosive ammo:  This ammo, most commonly found in military surplus cartridges, contains corrosive salts in the powder or primer.  Regular gun cleaning solvents will NOT remove the salts from the bore of the barrel, and the corrosion can ruin it.  Typically the corrosive chemicals must be removed with ammonia-based solvents, but it's best to just avoid it.
4. Use a multi-function solvent/lubricant:  The US military has relied on the combat-proven Break-Free CLP (Clean, Lubricate, Protect) for decades, and it works wonderfully.  I've recently become fond of Shooter's Choice FP-10, mostly because it smells a bit better.  I also have had good results from ClenzOil.  What all three of these products have in common, is that with a single liquid, you can clean your gun, keep it ready for action, and prevent rust.
   
   
5. Behold, the shaving brush:  A shaving brush is one of the best kept, secret gun cleaning tools around!  It's short, tough bristles let you sweep away dust and debris from hard to reach places, and it's short handle makes it ergonomic and maneuverable.
   
6. Clean regularly to prevent rust:  When I lived in Ohio and on southern Army bases, where the humidity is always high, it was necessary to clean unused guns monthly, or more, to keep them from rusting.  Here in Colorado, you can get away with less, but regular application of rust-inhibiting lubricants will keep the red monster at bay - a light coat is all it takes.
7. Don't forget to clean the magazines:  Magazines contribute one of the largest sources of malfunctions to the gun.  During every cleaning session, use a lightly lubricated rag to wipe the outside, feed lips, and follower of all your magazines.  Periodically, disassemble the magazines for a thorough internal cleaning.  Discard and replace any magazines that cause repeated malfunctions.
   
8. Scrape off the carbon:  Carbon will build up on internal gun parts, such as the bolt, and must be forcibly removed.  This is especially true on AR-15 style rifles, that use the "direct gas impingement" method of operation.  It looks like chipped, hard black paint, and should be scraped free with a non-damaging tool, such as the bronze scraper on the Leatherman MUT.
   
9. Read the manual:  This one sounds like another "DUH" bullet point, but it's good advice.  A quick read of the manual will most likely teach you exactly where the engineers that designed your gun want you to clean and lubricate it.  This not only makes certain that you're spending time on all the right parts, but it also saves you time that you would have wasted working on less critical areas.
   
10. Prevent rust on easily overlooked parts:  Even on guns that are mostly polymer and stainless steel, such as the S&W M&P pistols, there are many parts that are still steel.  What's worse, any steel parts that have engraving, scratches, or grip checkering/cuts/grooves will rust quickly, especially if you touch them often during operation.  Areas to pay special attention to are grooved safeties and fire selector levers, engraved serial number plates, slide and bolt stop levers, grip cuts on pistol slides, etc.  Let a drip of rust-inhibiting oil soak down into these features, and wipe off the excess.
    

With proper cleaning and maintenance, your firearm will last for decades, maybe even centuries.  Always be sure to put safety first, when handling and cleaning your guns, and put all ammunition in another room when performing cleaning.