Much depends on the kind of breach that you have. If you have a patent breach, you will need something that will get down in the small part. A small breach scraper such as a .32 to a .40 will get down in there and clean out the crud. If you have a "standard" breach, you can buy breach scrapers that are caliber specific to get out the crud. There are also brushes that screw onto the rod that are designed in such a way that they can be twisted against the breach and scrub off the crud. Once you get it clean, you can keep it clean by using the good old soapy water flush method to clean it. That will wash out all of the crud after each day at the range or trip to the woods.
If that crud has been in there for a while and has built up and baked on, you will need to soak it good to soften it up so you can get it out. To do this, just use something to plug the nipple or touch hole and then stand the rifle or just the barrel up where it will be safe and secure and then fill it with soapy water and let it sit for an hour. Empty out the soapy water and replace it with some clean soapy water. Let it sit again for an hour. Pour out this batch of soapy water and then set the breach in a container of soapy water and scrub with a tight fitting patch on your jag allowing the soapy water to flush in and out of the nipple hole (with the nipple out, of course). Quite often, this will remove even old crud. Once it is clean, keep it clean and the problem will not re-occur.
After washing out the bore, wipe it dry with several dry patches and then you can either spray the bore with WD-40 to remove the last traces of moisture or you can pour denatured alcohol into the bore to flush out any moisture. I think the WD-40 is better, though. Wipe out the bore again with dry patches to remove the WD-40 (it will have done its job) or the last traces of alcohol, if you use it. Once the bore is nice and dry and clean, put some Barricade on a patch and swab the bore well and it is ready for storage until the next time. Of course, you need to clean the rest of the gun, I am only addressing the cleaning of the bore.