ok...i have some experience with this. actually a good amount of experience. only i dont do what was suggested in the original post. i actually do stand with a cardboard sign. It says "will work for food". there are many variables that you can work on to increase your take.
-stand by a roadway where a large number of vehicles will pass by you and have to stop at a light for some amount of time longer than just a few seconds. it is important to have as many people see you with your sign as possible because the more people who see you means the more likely it is that someone will decide to "donate". it is important that people feel safe when giving money, which is why it is good to work a stoplight, because they are safe in their cars and can always just drive away. this also stops people from asking you a bunch of annoying questions such as why are you here and are you on drugs, because when the light changes they have to drive away. it also makes your job easier and reduces the occurences of people getting pissed and yelling at you. although this still happens occasionally. sometimes people will yell at you and tell you to get a job or call you a piece of shit. i have had people throw pennies or garbage at me, but the confliccts never escalate beyond a few second encounter because when the light changes they have to drive away.
sometimes people do try to solicit sex from you. for some reason i am attractive to gay men and have recieved alot of offers, which is a rather disturbing part of the job. do not look dramatically sad because people willl be repelled by this.
dont look like you are a total crackhead but dont look like you had a whole wardrobe to choose your clothes from. do have a story ready that is sad but not overdone and is believable in case someone wants to hear something before they fork it over. dress in bright colors but white or grey or light pastels not red or orange or yellow.
go sometime after morning rush hour (people are grumpy and in a hurry to get to work in the morning) and go before it is dark (people are more afraid of being robbed after dark). rain will totally fuck your day up. you cant look needy wearing a raincoat or holding an umbrella, and even though you would think they would feel bad seeing you stand there getting fucking soaked, they dont want to get wet themselves when they put down the window to give you whatever. most people give you money not because they want to help you, but because they want to feel good about themselves and reinforce their own belief that they are a good and generous person.
actually one of the worst things that can happen to you is a person who actually does care about you, because these are the people who will pull over and park and try to bring you into a restaurant and buy you food, or will try to take you home with them or take you to a homeless shelter or waste all your time finding out your life story which is actually a huge web of lies that you weave as you try to get them to move on. sometimes in a great while you can spend some time on these people and if you can get them to believe that you are down on your luck and not a junkie they will give you some larger sums of money, but a majority of people are not worth the time.
sometimes people will give you food, so you should have a place to hide any food you get until you are ready to leave. since you are relying on people to boost their own self worth through you, you will want to act like you are blown away by the fact that they have just given you a dollar and you are nominating them for a nobel prize. instead of a panhandler you could think of yourself as a kind of freelance self-esteem therapist. dont come off to desperate because to most people desperation means potential violence.
try to choose a spot where you have a good view of where all traffic is coming from so you can see if a cop is approaching and have time to fold up your sign and escape. it is good to go up a well trafficked one way street against the flow to ditch the cop because they dont usually want to catch you badly enough to go out of their way. if you do let a cop get close to you, some will do nothing, some will tell you to get lost, some may take your sign and yell at you. you can be locked up but most cops dont want to bring someone back to the station for panhandling and waste everyones time.
despite all the things that you can do to increase your chances some days will be good and some will be bad for no apparent reason. i have made hundreds in a few hours and made not even ten dollars in 5 or 6 hours. just do your best and be patient. you may make nothing in the first hour or so and then end up cleaning up later on. i think it has something to do with the quality of people driving by you at a certain time. for instance you can do very well on a sunday morning when people have just gotten out of church or around the holidays when people want to be all jolly and giving.
now i know some people are saying "how can you live with yourself lying to people for their charity" well two things help: telling yourself that they are actually doing it not so much to help you, but to help them feel better about themselves. its easier to give a few bucks to a panhandler every so often than to go volunteer at the soup kitchen on your day off or after work, but they are still fulfilling that need to be seen as a good person. and two: doing a bag of dope first. i always tried to panhandle when i was high because it basically kills any feelings that you have that say : this is wrong. but something tells me that if you are a drug addict you dont have to many moral dilemmas in which your conscience beats your desire to poke yourself with a needle full of heroin. and i would rather feel a bit ashamed for lying and hurting really no one than going into sears and filling a bag with 5 fucking power drills, and then going to jail for retail theft. as i explained, most people will be happy that they have given you money, and if they dont want to they have the option of driving away and forgetting they ever saw you.
well that about wraps it up, oh yeah highway off ramps are a good choice of location, so happy panhandling and dont go near my spots if you live in or around philly

, who knows i may need to use them again some day, you cant stay clean forever (well i cant). peace.