Payments for jobs

I'm making a bit of a push to seek paid work - just in order to pay my annual studio rent (so not a lot needed really but it does need to pay for itself)
I'm a bit lacking in the professional aspect - I need a little advice as regards contracts, when payment is requested etc
Basically I'm asking what is your route for a job where you get paid?

I did one job for a local glassware company and they loved the images - I sent samples - they took 3 weeks to explain that they were perfect but unfortunately they'd sold out of that line now. So I've kind of written that shoot off. My fault entirely. He delivered some more yesterday and I really enjoyed taking the images last night and have some great stuff for him....and have sent heavily watermarked images and asked for payment.

So I need to fine tune this process.

Im thinking:-
Job enquiry comes in;
Reply saying I can do it and give a rough estimate;
Client picks date;
Contract issued;
Shoot;
Invoice sent;
Payment received;
Images sent

How do you do this in a not quite so clinical way?