I am a learner busker myself, playing the concertina rather than singing (which I am better known for!), and I have only been out a few times so far. But I have taken the time to speak to two experienced musicians, one a classical violinist who busked all over Europe as his main income and the other a folk concertina player, who has tried all over the UK. They gave me a lot of tips:-

stand rather than sit, even when playing the concertina;
don't show that you are well off (no gold necklaces, Gucci shoes or the latest mobile phone) but don't dress in tatters either;
look as if you are enjoying it, seek eye contact and look friendly;
play the more upbeat or well know tunes in your repertiore when you have the biggest audience;
position yourself at pinch points so that the public cannot walk on the other side of the road;
have your back to a wall or where you can get the sound to carry;
avoid too outlandish clothes (you don't want the public to think you are an aged hippy and that you would immediately spend their money on booze or drugs!);
the best takings are in smaller market towns rather than the big cities where the public will associate you with the beggers they often see;
don't place yourself where there is a very big flow of people but you do need a steady flow, of course;
unless you have a big circus type act don't concentrate on the big shows in the major tourist spots (the competion can be too fierce!)
do hour long shows rather than longer as the local traders will get fed up, no matter how good you are (and so will you)
mornings are better than afternoons and after 3pm can be dismal
evenings are worth a try in the summer when people are out promenading
stick at it!

"I can laugh, dance and sing ..."
Alan