OK were do i start about this type of work lol. First and foremost you must understand that there is a huge difference between a bicycle courier and someone who loves to cycle now and then. You have got to be seriously fit, as the job could involve you cycling from one end of a city to the next and then all the way back again all day long lol. And if the physical demands aren't enough then you have to contend with motorists who simply could not give a shit if they knock you off your bike or not!!!! You will come home every evening covered in dirt and grit so you Better not be to self conscious lol, And lets not forget the sore back from carrying a bag all day. If you really would like to do this job then there are some key points which i have listed for you.
.You need a proper bike with brakes that work.
.You need a helmet a cycling gear although trakkies would do fine.
.Good geographical knowledge of the area.
.Be super fit.
.Super confident as you will be cycling among traffic.
You can make good money from this type of work if you look around many companies pay good money others not so good. I know a person who done it and they got £2.50 per letter parcel delivered, it dos,nt sound much but if you deliver four parcels an hour thats £10.
Good luck anyway you'll need it this is a dog eat dog environment. The faster you are the better you are simple as that.