I was very naive when I started sending out the manuscript of my novel. I believed the major publishers when they demanded exclusivity. I sent my proposal to one of them and waited the six months for the rejection. After a year and two rejections I realised that I would be published postumously if I continued like this. That's when I worked things out (I'm a bit slow, I'm affraid!). If everybody did the right thing, those famous writers who sent their work to a hundred and sixty publishers before getting recognised, must have spent sixty years just sending out proposals. I don't think so!
So, best of luck next time, Lisa F