How do i start up a dog walking business?

My best friend and i are very responsible and would like to take up a dog walking business for a bit of extra pocket money. We are both 13 years old and we own two very reliable dogs. ~How should we advertise ~How much should we charge ~How long should we walk them for please answer as we would very much like to find out about this before we start. i was just wondering what peoples views were and how much they would be willing to pay if they were looking for a dog walker.
advertise in newsagents,post offices,hand out flyers,put up posters,tell people to spread the word etc etc etc I would charge 7 or 8 pounds for 1hour walk to begin with.(5 pounds for 10/15 minutes is ridiculous! keep the dogs on a lead unless you have a small enclosed area(park, maybe?) near you which you can let them off in. BUT YOU MUST HAVE OWNERS PERMISSION BEFORE YOU LET THEM LOOSE!!!!!! good luck!