If you ever want to freak a non-musician out, show them a glob of the green slime that comes out of your trumpet when you clean it for the first time in months. My wife shuddered the first time she saw it, "You put that up to your mouth?!?" (My kids, however, thought it was hilarious.)
Yes, there are times when I do not keep my horn as clean as it should be, but there is no real excuse for that. Your trumpet is like a car—you must take good care of it if it is going to perform for you at top level when you need it. The best thing you can do is keep a full supply of all the necessary trumpet cleaning products right in your case so they're always nearby, especially after a performance. Here's what every trumpet player needs to have:
Cleaning Cloth—One task that should happen after every practice session or performance is a simple wipe-down of your horn's exterior. The residue, dirt and acids from your fingers will not only cause your lacquer to tarnish over time, but it can actually begin to eat through the trumpet's metal. Using a quality instrument cleaning cloth, like this one from Yamaha, is ideal. (Careful not to use just any cloth – some cloths can actually contain abrasive material!)
Snake—No, not a live one. Using a cleaning snake is an essential part of cleaning your horn. Nothing will get all the goop out better. Simply run it through your horn's tubing (after you've taken the horn apart) and it will pick up all the morsels from the pizza you ate on last month's session break. Be sure to run warm water through the horn afterwards. Check out this industry standard Micro Snake for your trumpet or cornet, or these ones from Herco and H.W..
Cleaning Rod—Attaching a small instrument cloth to a trumpet cleaning rod is a great way to do a quick cleaning of your lead pipe (where most of your, uh, "stuff" first collects) after a gig, since you won't always have time to do a full snake treatment. Remove your tuning slide and slip the rod on through. A cleaning rod is also very helpful when your horn is apart for getting into some smaller areas of your horn. Here's a good horn cleaning rod from Selmer.
Mouthpiece Brush—Simply a "must have" after every gig. A quality mouthpiece brush will help keep your tone pure and your pitch right. It's amazing how much stuff collects in your horn's mouthpiece and how easy it is to get it clogged up. Not only will that stuff eventually end up in your horn, but the more stuff that's in there, the more it affects your playing. Here's a mouthpiece brush from Protec that does a fine job cleaning brass instrument mouthpieces.
Slide Grease—While it's not exactly "cleaning," maintaining the lubrication on your brass instrument slides is a key part of maintaining and caring for your horn. Once they're stuck, it's often too late and you may need a professional repairman to loosen your slides. You can't get a better deal than Brasswind's own slide grease in a convenient lipstick-style tube.
Spitballs—While not exactly "standard fare" for a cleaning regimen, I personally love these Spitballs from Herco that remove the dirt that other brass instrument cleaners leave behind. They're a great way to clear any simple obstructions and an even greater way to annoy that trombone player sitting in front of you. (Don't tell them I told you to do it!)
Remember, your horn is an investment, whether you use it for a profession or for enjoyment. Take care of it well and it can give you many years of enjoyment.
So, let's keep it clean, and come out fighting!